Just in time for the holidays, when cozy and comforting are must-haves on the menu, these French Onion Steak Crostini hit all the right notes. We’re talking smoky filet mignon, sweet caramelized onions, creamy horseradish, and crisp bread toasted golden brown over the fire.
It’s the kind of perfect appetizer that looks a little fancy but still tastes like it was made next to the flames. Rustic, rich, loaded with flavor, and yeah… so freakin’ delicious, they’ll be gone before you even grab your second one.
Why You’ll Love French Onion Steak Crostini
If you love the comfort of French Onion Soup and caramelized onions, you’ll love this Italian-inspired appetizer. These steak crostini hit all the right notes: sweet, savory, creamy, and smoky. The caramelised onions bring that deep sweetness you get from cooking low and slow, while the steak adds a rich, beefy flavor that ties it all together. A dollop of horseradish cream cuts through the richness, and a sprinkle of melted gruyere adds an insane amount of simple indulgence.
It’s a simple cooking process that takes a bit of time but pays off in every bite. Filet mignon is a little bit fancy, but worth it for the melt-in-your-mouth results. Trust me, once you make this recipe for your next holiday spread, you’ll be thinking about making it again.
If you’re craving more crostini action, check out my Grilled Steak Crostini next — smoky, simple, and straight fire. Or dive into my Best Grilled Appetizer Recipes for more bites that bring the heat to your next cookout.
A Little History on Crostini
Crostini might sound fancy, but it’s actually one of the oldest and simplest ways to enjoy good food. The word literally means “little toasts” in Italian, born out of the idea that nothing should go to waste. Farmers and cooks would toast up leftover bread over an open flame, then pile on whatever they had: meat, cheese, or roasted vegetables. Simple, rustic, and straight from the fire. That’s what makes it such a perfect fit for this recipe, since it’s a nod to old-school cooking with a modern, over-the-fire twist.
Ingredients Round-Up
- Steak – Your favorite steak cut, Cowboy Butter Rub or steak seasoning, olive oil, garlic cloves, fresh thyme, rosemary, butter, and black pepper.
- Caramelized Onions – Thinly sliced white or yellow onions, beef broth, bourbon, salt, black pepper, and olive oil.
- Horseradish Cream – Mayonnaise, sour cream, prepared horseradish, Dijon mustard, and champagne vinegar or red wine vinegar.
- Crostini – Baguette slices, olive oil, grated gruyere cheese, chopped chives for garnish.
Bring the Flavor Home
Get ready, because these French Onion Steak Crostini are next-level decadent. It doesn’t get much better than smoky, buttery steak layered with sweet caramelized onions, tangy horseradish cream, and melted gruyere on crisp golden bread. It’s the perfect bite that I can’t wait to show you how to make.
How to Make French Onion Steak Crostini
Onion Prep
Start with the caramelized onions. Heat a cast iron skillet or large skillet over medium-high heat and drizzle in a little olive oil. Add your sliced onions and season them with salt and black pepper. Let them cook slowly, stirring often, shifting between medium and low heat to prevent burning.
This takes some patience — about 45 to 60 minutes — but the result is worth it. When the onions turn deep brown and soft, deglaze the pan with bourbon and beef broth. Let it simmer for 3 to 5 minutes until the liquid cooks down. Keep warm.
While the onions are finishing, season your steaks with Cowboy Butter Rub, olive oil, and black pepper. Let them rest at room temperature for 15 to 20 minutes before cooking.
Grilling Time
Preheat your grill to medium-high heat, around 375°F. Drop a cast iron skillet on the grates and let it heat for 2 to 3 minutes. Add a little oil, then sear the steaks for 1 to 2 minutes per side until a crust forms.
Move the skillet to a cooler part of the grill (or raise up your grill grates on the Santa Maria) and toss in butter, garlic cloves, and fresh thyme. Let them sizzle for 30 seconds, then start basting the steaks with the melted butter. Keep basting until the internal temperature hits about 120F for medium rare steak.
Pull the steaks off, drizzle the butter and herbs over the top, and let them rest while you toast the bread.
The Build
Slice your baguette into half-inch slices and brush each side with olive oil. Lower the grill heat to 300F and toast each slice for 2 to 3 minutes per side until golden brown. You can also bake them on a sheet pan lined with parchment paper if you prefer.
Slice your rested steak into thin slices. Spread a layer of horseradish cream on each crostini, then top with a spoonful of caramelized onions and a slice of steak. Sprinkle grated gruyere over the top and add chopped chives. Finish with a pinch of fresh parsley and serve warm.
What to Serve It With steak crostini
These crostini are perfect with a pour of bourbon or a glass of red wine. The richness of the steak and onions plays beautifully against smoky drinks or deep reds. You can also serve them alongside a fresh green salad or roasted vegetables if you want to balance things out.
Leftovers & Reheating
If you’ve got leftovers, store the onions, steak, and horseradish cream separately in airtight containers. Reheat the onions and steak gently over medium heat or in a skillet for a few minutes, then toast new bread slices and rebuild your crostini. The flavors only get better the next day.
More French Onion Recipes
Crostini FAQs
Absolutely. Use whatever steak you’ve got or love. Ribeye, filet mignon, and even flank steak work great. Just season it up, cook it hot and fast in that cast iron skillet, and shoot for a perfect medium rare. And don’t forget, a digital meat thermometer helps nail that temp every time.
For sure. The onions take a little time, so make them first and stash them in the fridge. You can also whip up the horseradish cream a day or two ahead. When it’s go time, reheat the onions over medium heat, toast your bread, and slice your steak fresh off the fire. Easy.
Gruyere gives it that classic French onion soup flavor, but if you want to mix it up, aged cheddar is a great option. Melt it right on the grill or pop them back on a warm sheet pan for 2-3 minutes, or until the cheese is nice and bubbly.
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French Onion Steak Crostini
Ingredients
Steak:
- 2-3 Filet Mignons
- 2-3 tbsp Cowboy Butter Rub
- 3 Rosemary Sprigs
- 3 Thyme Sprigs
- 3 Garlic Cloves smashed
- ½ cup Unsalted Butter
- Canola Oil as needed
Caramelized Onions:
- 2 medium White Onions thinly sliced
- ⅛ cup Beef Broth
- 2 oz Bourbon
- Salt & Pepper to taste
- 2 tbsp of Canola Oil
Horseradish Cream:
- 2.5 tbsp Sour Cream
- 2.5 tbsp Mayonnaise
- 2 tbsp Prepared Horseradish
- 1 tbsp Dijon Mustard
- 2 tsp Champagne Vinegar or white vinegar
Crostini:
- 1 Whole Baguette sliced into ½” pieces
- 1 cup Olive Oil
- Chopped Chives for garnish
- Grated Gruyere Cheese for garnish
Instructions
Onions:
- Preheat your grill to medium high heat (about 350F) for direct cooking. Add a cast iron skillet to the grill 2 minutes before cooking.
- Add oil in the skillet and add your thinly sliced white onions. Season the onions with salt and pepper and begin cooking on a medium heat until they are caramelized (dark brown). This should take about 45-60 minutes to achieve. Stir frequently and move from high heat to prevent them from burning.
- Once they are dark brown and soft, deglaze the skillet with bourbon and beef broth. Let simmer until most of the liquid is gone (about 3-5 minutes). When the onions are done, pull off and keep warm.
Steak & Crostini:
- Slather your steaks with oil and generously seasoning Cowboy Butter Rub (or your favorite steak seasoning) all over. Set to the side until ready to cook.
- In another bowl, mix together the Horseradish Cream Sauce and set in the fridge until ready.
- Preheat a medium high heat fire for direct cooking (about 375F). Add a cast iron skillet about 2-3 minutes before cooking with some oil to preheat.
- Once the skillet is hot, add your steaks to sear for 1 minute per side to develop a crust. Next, pull the skillet over to a cooler side of the grill or raise your grill grate.
- Add in the rosemary, thyme and crush garlic to simmer for 30 seconds. Finally add in butter and let it melt.
- Push your steaks to one side of the skillet and place the herbs and garlic on top. Begin basting the steak with the butter continually for 2 minutes then flip. Repeat this until your steaks have reached 120F internal. Be careful of your heat so the butter does not burn!
- Once the steaks are done, pull them off and the steaks with the herbs and drizzle all the butter over top. Let rest until ready to slice.
- Next, slice your baguette into ½” slices. Brush each slice of bread with olive oil on both sides. Next, lower the heat of the grill to 300F and add each slice of bread to cook for 2-2.5 minutes per side or until they are toasted/golden brown. Once done, pull the bread off and set to the side until ready to serve.
- Slice your steaks into thin cut pieces and begin building your Crostini. Build your crostini with bread, horseradish sauce, onions, sliced steak, grated cheese and chopped chives. Serve and enjoy!
