Name: Grilled Steak Sandwiches with Caramelized Onions, Brie, and Horseradish Sauce Recipe
Prep time: 15 min
Cook time: 35 min
Total time: 50 min
Cuisine: American
Ingredients: 1/2 cup mayonnaise; 1 tablespoon prepared horseradish; 2 teaspoons Dijon mustard; 2 teaspoons Worcestershire sauce; 2 tablespoons minced chives; 1/2 teaspoon lemon zest; 2 tablespoons lemon juice; 1/2 teaspoon freshly cracked black pepper; Salt, to taste; 1 1/2 lbs flat iron steak; 2 tablespoons salted butter; 2 sweet Vidalia onions, thinly sliced; 10 oz triple cream brie, sliced; 3 cups arugula; 6 radishes, sliced; Kosher salt, to taste; Freshly cracked pepper, to taste; Sandwich bread, such as rustic or sourdough, 12 slices (for 6 sandwiches)

Jump to Recipe· 3.9 from 2 reviews

I absolutely adore the rich flavors and satisfying textures packed into this Grilled Steak Sandwiches with Caramelized Onions, Brie, and Horseradish Sauce Recipe. Every bite brings together savory, creamy, tangy, and peppery notes that feel so indulgent yet perfectly balanced. It has become one of my favorite go-to sandwiches when I want something special that feels gourmet but is still delightfully easy to prepare at home. Sharing this recipe feels like sharing a little joy on a plate.

Why You’ll Love This Grilled Steak Sandwiches with Caramelized Onions, Brie, and Horseradish Sauce Recipe

I must say, what makes this sandwich so irresistible to me is the beautiful harmony of flavors. The caramelized onions bring a luscious sweetness that cuts through the bold, tender steak slices, while the triple cream brie adds a luxurious, melty creaminess that ties everything together. The horseradish sauce gives it a gentle kick of heat with a tangy bite, awakening your palate in the most delicious way. I find every element thoughtfully layered yet balanced perfectly.

Besides the taste, I really appreciate how straightforward this recipe is. It feels like a restaurant-quality sandwich experience without complicated steps or obscure ingredients. Plus, it fits brilliantly into many occasions — whether I’m throwing a casual dinner with friends or craving a satisfying weeknight meal. The fresh arugula and radishes add just the right crunch and peppery freshness, elevating the sandwich beyond your everyday steak sandwich. It’s a standout, wedding my favorite indulgences into one plate.

Ingredients You’ll Need

A single piece of raw red meat with white fat lines lies centered on a rich brown wooden cutting board with a patterned texture. To the left of the meat, there is a small round wooden bowl filled with coarse white salt, with some salt spilled beside it. On the right side, a large shiny silver knife rests diagonally on the board, pointing towards the top right corner. Above the knife, a bunch of fresh dark green herbs is placed. At the top center of the image, a tall dark pepper grinder is visible. The cutting board sits on a white marbled surface. Photo taken with an iphone --ar 4:5 --v 7

The ingredients for this Grilled Steak Sandwiches with Caramelized Onions, Brie, and Horseradish Sauce Recipe are delightfully simple but essential, each playing a vital role in texture, flavor, and color. From the rich creaminess of the brie to the fresh bite of arugula, every item is chosen to create harmony in each sandwich bite.

Mayonnaise: Creates the creamy base for the horseradish sauce, adding smoothness and richness.
Prepared horseradish: Packs a zesty, slightly spicy punch that livens up the sauce exquisitely.
Dijon mustard: Adds a subtle sharpness that deepens the flavor complexity of the sauce.
Worcestershire sauce: Provides an umami boost and a hint of savory depth to the sauce.
Minced chives: Offers a mild oniony freshness that brightens the horseradish sauce.
Lemon zest and juice: Impart brightness and acidity, balancing the richness throughout the sandwich.
Freshly cracked black pepper: Adds aromatics and gentle heat to season the steak and onions.
Salt: Critical for enhancing all the flavors from steak to onions to bread.
Flat iron steak: A tender, flavorful cut that grills beautifully and slices thin for the sandwich.
Salted butter: Essential for caramelizing the onions and adding a luscious richness.
Sweet Vidalia onions: Their natural sweetness caramelizes perfectly for depth and texture.
Triple cream brie: Melts to a silky texture, creating a creamy contrast to the steak.
Arugula: Brings a peppery freshness and crisp texture that lifts the sandwich.
Radishes: Thinly sliced for crunchy, spicy notes that add dimension.
Kosher salt: Used to finish and season the sandwiches for the perfect bite.

Directions

Step 1: Start by melting the salted butter in a skillet over medium heat. Add the thinly sliced sweet Vidalia onions and toss them well in the butter. Season lightly with salt and freshly cracked pepper. Cook the onions slowly, stirring occasionally, until they turn a deep golden brown, which should take about 25-30 minutes. Set them aside once caramelized.

Step 2: Meanwhile, whisk together the horseradish sauce ingredients: mayonnaise, prepared horseradish, Dijon mustard, Worcestershire sauce, minced chives, lemon zest, lemon juice, and black pepper until smooth and well combined. Cover and refrigerate this sauce until you’re ready to assemble your sandwiches.

Step 3: About 30 minutes before grilling, take the flat iron steak out of the refrigerator and season all over with salt and pepper. Allow it to come to room temperature so it cooks evenly.

Step 4: Preheat your grill or grill pan over medium-high heat. Grill the steak for 4-5 minutes per side if your steak is on the thicker side for a perfect medium-rare to medium doneness. For thinner steaks, aim for 3-4 minutes per side. Adjust accordingly if you prefer your steak more done. Once cooked, transfer the steak to a plate, cover loosely with foil, and let it rest for about 10 minutes before slicing.

Step 5: Slice the rested steak thinly against the grain for maximum tenderness. If you’d like, sprinkle a little flaky sea salt on the sliced steak to boost its natural flavors.

Step 6: While the steak is resting, grill your sandwich bread cut-side down on the grill for 1-2 minutes, just until it’s lightly toasted and gets those gorgeous grill marks.

Step 7: Now comes the fun part: assembling your sandwiches. Spread a generous amount of horseradish sauce on both halves of your grilled bread. Layer on the caramelized onions, thinly sliced steak, slices of triple cream brie, fresh arugula, and finally the thin radish slices. Top with the other bread slice and serve immediately while everything is warm and melty.

Servings and Timing

This recipe makes 4 hearty servings, perfect for sharing with friends or family around the table. Prep time generally takes about 15 minutes, mostly for slicing and mixing the horseradish sauce. The caramelized onions take around 30 minutes and can be made ahead to save time. Cooking the steak and assembling sandwiches requires roughly 10-15 minutes. In total, expect about 50 minutes from start to finish. The steak benefits from a short resting period after grilling, so plan to let it rest 10 minutes to keep it juicy and tender. This timing ensures a perfectly balanced and delicious sandwich experience.

How to Serve This Grilled Steak Sandwiches with Caramelized Onions, Brie, and Horseradish Sauce Recipe

A wooden cutting board with a rich brown and natural wood grain pattern holds a piece of sliced meat. The meat has two parts: one side shows seven thin slices with a red center and browned edges, and the other side has three thicker slices with a more cooked brown outer layer and pink inside. The right side has an unsliced cooked piece of meat with a browned surface. A large silver knife lies diagonally on the board, and a small brown bowl filled with coarse salt is placed on the left edge. The cutting board sits on a white marbled surface. Photo taken with an iphone --ar 4:5 --v 7

When I serve this sandwich, I like to keep the accompaniments simple yet complementary. A crisp green salad with a lemon vinaigrette pairs wonderfully, enhancing the fresh peppery arugula and cutting through the rich brie. Roasted baby potatoes or a light slaw also make fantastic sides if you want a fuller meal. For presentation, I like to slice the sandwich in half and display the layers so the vibrant colors peek through — the golden onions, rosy radishes, and deep pink steak look stunning.

Beverage-wise, I often reach for a bold red wine like a Cabernet Sauvignon or Malbec that stands up to the savory steak and melts with the creaminess of the brie. For a non-alcoholic option, sparkling water with a splash of lemon is refreshing and keeps the palate bright. This sandwich truly shines when served warm, just off the grill, so the cheese melts perfectly and the flavors meld together beautifully. I recommend plating it immediately after assembly for the best taste and texture.

This Grilled Steak Sandwiches with Caramelized Onions, Brie, and Horseradish Sauce Recipe is ideal for everything from a casual weekend lunch to an impressive dinner when entertaining. It feels decadent without fuss, making it my favorite “small celebration” meal any time the craving strikes.

Variations

I often experiment with this recipe depending on what I have on hand or to suit different tastes. One easy substitution is swapping the flat iron steak for ribeye or sirloin if you prefer a fattier or leaner cut. For the cheese, while triple cream brie is my favorite because of its meltiness and richness, a creamy Camembert or mild goat cheese would also offer a delicious twist.

If you are following a gluten-free diet, try using gluten-free sandwich bread or hearty gluten-free buns — they grill nicely and hold up well to the juicy fillings. For a vegan twist, I’ve had great success using a plant-based steak substitute, vegan mayo, and a cashew-based creamy cheese alternative paired with caramelized mushrooms instead of onions, which gives a rich, umami-packed flavor profile.

For a different flavor twist, consider adding fresh thyme or rosemary to the caramelized onions or swapping horseradish sauce with a garlic aioli for a softer, richer sauce. You can also toast the bread in a panini press instead of on the grill for a crunchier exterior. All these variations give you creative freedom while preserving the delicious essence of this classic sandwich.

Storage and Reheating

Storing Leftovers

If you happen to have leftovers, I recommend storing the sandwiches unassembled in separate airtight containers — keep the steak and caramelized onions refrigerated in one container, the horseradish sauce in a small jar, and the bread wrapped tightly to maintain texture. The arugula and radishes are best added fresh when serving again. Stored this way, the components will stay fresh for 2 to 3 days in the refrigerator.

Freezing

Freezing fully assembled sandwiches isn’t ideal because of the delicate fresh vegetables and soft cheese, which can get watery or lose texture. However, you can freeze the cooked steak and caramelized onions separately in freezer-safe containers or bags for up to 2 months. Thaw them overnight in the fridge before reheating and assembling the sandwich fresh for best results.

Reheating

To reheat your leftover steak and onions, gently warm them in a skillet over low heat until heated through to avoid overcooking the meat. Reheat the grilled bread separately in a toaster oven or under a broiler for a minute or two to restore its crispness. Avoid microwaving assembled sandwiches as that can make the bread soggy and the cheese rubbery. Then, assemble with fresh arugula, radishes, and horseradish sauce to bring back the vibrant flavors and textures.

FAQs

Can I use a different cut of steak for this recipe?

Absolutely! While flat iron steak is perfect because of its tenderness and flavor, you can substitute ribeye, sirloin, or even flank steak. Just adjust the cooking time depending on thickness and desired doneness to keep the meat juicy and flavorful.

How long can I keep the horseradish sauce in the fridge?

The horseradish sauce stays fresh and flavorful for up to 5 days when stored in an airtight container in the refrigerator. It’s best made ahead since the flavors meld beautifully the longer it sits.

Can I prepare the caramelized onions in advance?

Yes! Caramelized onions actually taste even better when made a day ahead because the flavors deepen. Just store them in an airtight container in the fridge and gently reheat when ready to use.

What type of bread works best for this sandwich?

I prefer using a rustic country bread or a crusty baguette because they hold up well to grilling and the moisture from the sauce and steak. You want a bread with some chew and crispness to complement the tender fillings.

Is there a good vegetarian alternative to the steak in this recipe?

Definitely! Grilled portobello mushrooms or marinated tofu slices can work wonderfully as substitutes, providing a hearty texture and flavor that pairs well with the caramelized onions and brie. For a vegan version, swap the brie and mayo sauce for plant-based alternatives for a satisfying sandwich.

Conclusion

I hope you feel as excited as I do to dive into this Grilled Steak Sandwiches with Caramelized Onions, Brie, and Horseradish Sauce Recipe. It’s one of those dishes that thrills me every time I make it — packed with bold flavors, indulgent textures, and yet so accessible at home. Give it a try, share it with those you love, and savor every glorious bite!