Why You’ll Love French Onion Steak Crostini Recipe
I love this recipe because it layers so many bold flavors into one perfect bite. I get buttery steak, sweet and savory onions, crunchy bread, and a sharp, creamy sauce all working together. I also appreciate how flexible it is, since I can cook everything in advance and build the crostini right before serving without stress.
Ingredients
(Note: All ingredient amounts are listed in the recipe card below.)
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 canola oil
Crostini: 1 whole baguette, sliced into ½-inch pieces 1 cup olive oil Chopped chives for garnish Grated Gruyère cheese for garnish
Directions
I begin by preheating my grill to medium-high heat, around 350°F, and placing a cast iron skillet on the grill to preheat. I add oil to the skillet, then the sliced onions, seasoning them with salt and pepper. I cook them slowly, stirring often, for about 45–60 minutes until they are dark brown, soft, and deeply caramelized. Once ready, I deglaze the pan with bourbon and beef broth and let it simmer until most of the liquid cooks off, then I set the onions aside and keep them warm.
Next, I coat the steaks lightly with oil and season them generously with Cowboy Butter Rub. I mix all the horseradish cream ingredients in a bowl and place the sauce in the fridge until needed.
I heat the grill again to about 375°F and preheat another cast iron skillet with oil. I sear the steaks for about 1 minute per side to develop a crust, then move the skillet to lower heat. I add the rosemary, thyme, smashed garlic, and butter, letting everything melt and become fragrant. I baste the steaks continuously, flipping as needed, until they reach about 120°F internal temperature. I remove the steaks, spoon the butter and herbs over them, and let them rest before slicing.
For the crostini, I brush the baguette slices with olive oil on both sides and toast them on the grill at about 300°F for 2–2.5 minutes per side until golden and crisp.
To assemble, I spread horseradish cream on each crostini, add a spoonful of caramelized onions, top with sliced steak, then finish with grated Gruyère and chopped chives.
Servings and Timing
This recipe serves about 4 people as an appetizer. Prep time takes me around 30 minutes, cooking time is about 1 hour and 30 minutes, and total time comes to roughly 2 hours, with much of that being hands-off caramelizing and resting time.
Variations
When I want to change things up, I use ribeye or strip steak instead of filet for a richer bite. I sometimes swap Gruyère for Swiss or provolone, or add a touch of balsamic vinegar to the onions for extra depth. Toasting the crostini in the oven also works if grilling isn’t an option.
Storage/Reheating
I store the steak, onions, and sauce separately in airtight containers in the refrigerator for up to 2 days. I reheat the steak gently in a skillet and warm the onions before assembling. I always build the crostini fresh so the bread stays crisp.
FAQs
Can I make this recipe ahead of time?
I often prepare all the components ahead and assemble just before serving.
What steak works best for crostini?
I like filet for tenderness, but any good grilling steak works well.
How do I avoid burning the onions?
I keep the heat moderate and stir frequently, moving the pan if needed.
Can I cook this entirely indoors?
I can use the stovetop and oven with cast iron pans if grilling isn’t available.
How thin should I slice the steak?
I slice it thin so it’s easy to bite and fits neatly on the crostini.
Is the horseradish sauce spicy?
It has a gentle heat that balances the richness, but I can adjust it easily.
What bread works best?
I prefer a classic baguette sliced evenly for consistent toasting.
Can I skip the bourbon?
I can replace it with extra beef broth if needed.
How do I keep crostini crisp?
I wait to assemble until right before serving.
Is this good for entertaining?
I love it for entertaining because it looks impressive and serves easily.
Conclusion
French onion steak crostini is one of my favorite appetizers when I want something bold, comforting, and memorable. I love how each bite delivers rich steak, sweet onions, and crunchy bread with just enough creaminess to tie it all together, making it a dish I’m always proud to serve.
An elegant appetizer featuring tender filet mignon, deeply caramelized French onion-style onions, crispy crostini, and a creamy horseradish sauce for rich, bold, and satisfying bites.
Ingredients
2–3 filet mignon steaks
2–3 tablespoons Cowboy Butter Rub
3 rosemary sprigs
3 thyme sprigs
3 garlic cloves, smashed
1/2 cup unsalted butter
Canola oil, as needed
2 medium white onions, thinly sliced
1/8 cup beef broth
2 oz bourbon
Salt, to taste
Black pepper, to taste
2 tablespoons canola oil
2.5 tablespoons sour cream
2.5 tablespoons mayonnaise
2 tablespoons prepared horseradish
1 tablespoon Dijon mustard
2 teaspoons champagne vinegar or white vinegar
1 whole baguette, sliced into 1/2-inch pieces
1 cup olive oil
Chopped chives, for garnish
Grated Gruyère cheese, for garnish
Instructions
Preheat grill to medium-high heat (about 350°F) and place a cast iron skillet on the grill.
Add canola oil to the skillet and cook sliced onions with salt and pepper, stirring often, for 45–60 minutes until deeply caramelized.
Deglaze onions with bourbon and beef broth, simmer until liquid reduces, then set aside and keep warm.
Lightly coat steaks with oil and season generously with Cowboy Butter Rub.
In a bowl, mix sour cream, mayonnaise, horseradish, Dijon mustard, and vinegar. Refrigerate until ready to use.
Increase grill temperature to about 375°F and preheat another cast iron skillet with oil.
Sear steaks for about 1 minute per side until a crust forms.
Lower heat, add butter, rosemary, thyme, and garlic, and baste steaks until they reach 120°F internal temperature.
Remove steaks, spoon butter and herbs over them, and let rest before slicing thinly.
Brush baguette slices with olive oil and toast on grill at 300°F for 2–2.5 minutes per side until crisp.
Assemble crostini by spreading horseradish cream on bread, topping with caramelized onions, sliced steak, Gruyère cheese, and chives.
Notes
Components can be prepared ahead and assembled just before serving.
Slice steak thinly for easy eating.
Cook onions slowly to prevent burning.
Assemble crostini right before serving to keep bread crisp.
