Steak Crostini with Horseradish Sauce, Caramelized Onions tastes like steakhouse meets snack time: crisp baguette, juicy seared steak, sweet onion jam vibes, and a creamy, nose-tingly hit of horseradish. It suits game-day grazers, holiday hosts, and date night snackers who want an impressive appetizer done in about 45 minutes. I learned this combo at a dinner party years ago and still keep steak tips and horseradish stocked for “just-in-case” hosting.
Why Make This Steak Crostini with Horseradish Sauce
Steak Crostini with Horseradish Sauce, Caramelized Onions stays easy because you cook the onions while the steak rests and the baguette toasts. The horseradish sauce stirs together in one bowl with pantry staples. You juggle components without stress and plate it like a pro.
You also get flexibility with cut choice and timing. You can caramelize onions earlier in the day and warm them before assembly. That one move saves you a chunk of clock time.
Ingredients You Need
- Steak: 1 to 1.25 pounds sirloin, New York strip, or ribeye, about 1-inch thick. Thin skirt steak works too, just shorten the sear. Pat dry for best browning.
- Baguette: 1 large French baguette, sliced into 24 to 28 half-inch rounds. Use a good bakery loaf or a take-and-bake stick from the grocery store.
- Onions: 2 large yellow onions, thinly sliced.
- Fat for onions: 2 tablespoons unsalted butter + 1 tablespoon olive oil.
- Seasoning for onions: 1 teaspoon kosher salt, 1 teaspoon sugar (optional for jump-start), 1 to 2 teaspoons balsamic or sherry vinegar to finish.
- Horseradish sauce:
- Steak seasoning: 1.25 teaspoons kosher salt, 3/4 teaspoon black pepper, 1/2 teaspoon garlic powder.
- Finishes: Flaky salt, extra chives or parsley, tiny drizzle of olive oil. A handful of baby arugula adds a peppery layer if you like.
Pantry shortcuts and swaps:
- Use store-bought horseradish cream if time runs tight; stir in extra prepared horseradish for more heat.
- Sub onion jam for caramelized onions in a pinch; warm it so it spreads nicely.
- Use sliced deli roast beef when you need a no-cook route; warm it briefly in a skillet with butter.
Equipment:
- Cast iron or heavy skillet, sheet pan, chef’s knife, cutting board, tongs, small bowl, spoon, instant-read thermometer.
How to Make Steak Crostini with Horseradish Sauce
Prep 15 minutes | Cook 30 minutes | Total 45 minutes
- Season the steak: Pat the steak very dry. Mix salt, pepper, and garlic powder, then season all sides. Let it sit at room temp while you start the onions.
- Caramelize the onions: Heat a skillet over medium. Add butter and oil, then the onions and salt. Cook, stirring often, until deep golden and jammy, 18 to 25 minutes. If they brown too fast, lower the heat and splash in a tablespoon of water. Finish with sugar and vinegar if you want extra depth.
- Toast the crostini: Heat the oven to 375°F. Slice the baguette, brush both sides with olive oil, and place on a sheet pan. Bake until edges turn golden and centers feel crisp, 8 to 10 minutes.
- Mix the horseradish sauce: In a bowl, stir together sour cream, prepared horseradish, Dijon, lemon juice, chives, salt, and pepper. Taste and adjust horseradish to your heat level.
- Sear the steak: Heat a light film of oil in a clean hot skillet over medium-high until it shimmers. Sear the steak 2 to 4 minutes per side for medium-rare, flipping once. Aim for 125 to 130°F internal for medium-rare, or your preferred temp. Move the steak to a board and rest 5 to 10 minutes.
- Slice the steak: Slice thinly against the grain. Keep the slices bite-size so they sit nicely on the toasts.
- Assemble the crostini: Spread each toast with horseradish sauce. Add a forkful of caramelized onions, then a slice or two of steak. Finish with flaky salt, cracked pepper, extra chives, and a tiny drizzle of olive oil.
- Serve: Plate the steak crostini warm or at room temp. Watch them vanish like socks in a dryer.
Tips & Common Mistakes
- Dry the steak well before seasoning so you get a solid crust.
- Salt early so the seasoning sticks and the steak cooks evenly.
- Keep onion heat at medium to medium-low. High heat scorches and turns them bitter.
- Add a splash of water if onions look dry before they soften.
- Slice bread evenly so it toasts at the same rate.
- Start with less horseradish, then add more to taste. Some jars pack serious fire.
- Rest the steak, then slice against the grain for tender bites.
- Do not overload each toast. Balance sauce, onions, and steak so the bite stays tidy.
- Assemble close to serving so the crostini stay crisp. Shield with a small arugula leaf if you need to hold them a bit.
- Use a thermometer for perfect doneness every time.
Variations
- Blue cheese cream in place of horseradish sauce, plus a dab of fig jam.
- Goat cheese base with onions, steak, and a drizzle of honey.
- Chimichurri instead of horseradish sauce for a herb-forward bite.
- Peppercorn-crusted steak with a quick pan sauce for drips on top.
- Balsamic onion jam with shaved Parmesan and arugula.
- Swap in lamb, pork tenderloin, or portobello slices for a different twist.
- Use gluten-free baguette or toasted polenta rounds for a wheat-free base.
How to Serve Steak Crostini
Serve these steak crostini warm on a big board with extra horseradish sauce on the side. Pair with a bold red like cabernet or a lighter pinot noir, or pour a malty amber ale. Add crunchy pickles or a citrusy salad to cut the richness. If you want a full spread, set them next to shrimp cocktail and marinated olives.
Make-Ahead and Storage
Caramelize the onions up to 4 days ahead and chill in an airtight container; warm them on low before assembly. Mix the horseradish sauce up to 5 days ahead and keep it cold. Toast the crostini up to 2 days ahead; cool fully and store in a zip-top bag with most of the air pressed out, then re-crisp 3 to 5 minutes at 300°F if needed. Cook the steak the day you serve for best texture, though you can cook it 1 to 2 days ahead and slice; warm slices gently in a buttered skillet over low heat so they stay tender. Skip freezing assembled crostini; freeze caramelized onions for up to 2 months if you want a head start.
Nutrition Information
Approx per 2 crostini: 260 calories; 14g fat; 5g saturated fat; 17g carbs; 16g protein; 3g sugar; 470mg sodium. Estimates vary by steak cut, bread size, and sauce amount.
Steak Crostini with Horseradish Sauce and Caramelized Onions
Ingredients
Instructions
- Heat 1 tablespoon olive oil in a skillet over medium heat. Add sliced onions and sugar. Cook, stirring often, until onions are deep golden brown and caramelized, about 25-30 minutes. Season with a pinch of salt and set aside.
- In a small bowl, combine sour cream, horseradish, Dijon mustard, and lemon juice. Season with salt and pepper to taste. Mix well and refrigerate until ready to use.
- Rub steak with salt and pepper. Heat remaining olive oil in a skillet over medium-high heat. Sear steak for 3–4 minutes per side until medium-rare or desired doneness. Rest for 5 minutes, then slice thinly across the grain.
- Preheat oven to 400°F (200°C). Arrange baguette slices on a baking sheet and toast 5–7 minutes, flipping halfway, until golden and crisp.
- Spread each toasted baguette slice with a spoonful of horseradish sauce.
- Top with a slice of steak and a spoonful of caramelized onions.
- Garnish with chopped fresh chives if desired. Serve immediately.