Steak Crostini with Horseradish Sauce & Caramelized Onions – Elegant, Bite-Sized Flavor Bombs

Steak crostini with horseradish sauce and caramelized onions is the kind of appetizer that leaves a lasting impression. These elegant little bites combine tender slices of seared steak, rich and sweet caramelized onions, and a bold horseradish cream—all perched on crisp toasted bread.

Perfect for holiday parties, New Year’s Eve, or upscale game day snacks, these crostini deliver layers of flavor in every bite: smoky, creamy, sweet, and savory with just a touch of heat. They’re easy to assemble, endlessly customizable, and look beautiful on a platter.

Whether you’re hosting a cocktail party or looking for a showstopping starter, these steak crostini bring a touch of steakhouse indulgence into a bite-sized form.

Ingredients Overview

Steak

Use high-quality beef, such as:

• Ribeye – marbled and flavorful

• Sirloin – leaner and budget-friendly

• Filet mignon – for extra tenderness

Aim for medium-rare to medium doneness for optimal tenderness. Let the steak rest before slicing thinly against the grain.

Pro Tip: Pat steak dry before searing and season generously with salt and cracked black pepper.

Baguette or French Bread

The base of your crostini needs to be sturdy and crisp:

• Use a baguette, sliced into ½-inch rounds

• Toast in the oven with a brush of olive oil for golden edges and crunch

You can rub the toasted bread with a cut garlic clove for added aroma.

Caramelized Onions

Slow-cooked onions add a sweet, jammy richness that contrasts beautifully with the tangy sauce and savory steak.

Use yellow or sweet onions, sliced thin and cooked low and slow in:

• Butter or olive oil

• A pinch of salt

• Optional: a splash of balsamic vinegar or red wine for depth

Caramelizing takes about 30–40 minutes—make them ahead to save time.

Horseradish Sauce

The creamy, tangy bite of horseradish sauce cuts through the richness of the beef.

Make a quick sauce with:

• Sour cream or crème fraîche

• Prepared horseradish (adjust to taste)

• Dijon mustard

• Lemon juice

• Salt and pepper

Optional: add chopped chives or parsley for a fresh finish.

Garnishes (Optional)

• Fresh thyme or microgreens

• Shaved Parmesan

• Flaky sea salt for crunch

Step-by-Step Instructions

1. Caramelize the Onions:

   • Heat 1–2 tablespoons butter or olive oil in a skillet over medium-low.

   • Add thinly sliced onions with a pinch of salt.

   • Cook, stirring occasionally, for 30–40 minutes until golden and jammy.

   • Optional: Deglaze with a splash of balsamic or red wine. Set aside.

2. Make the Horseradish Sauce:

   • In a small bowl, mix 1/2 cup sour cream, 1–2 tablespoons prepared horseradish, 1 teaspoon Dijon mustard, and 1 teaspoon lemon juice.

   • Season with salt and pepper. Chill until ready to use.

3. Prepare the Crostini:

   • Preheat oven to 375°F (190°C).

   • Slice baguette into ½-inch rounds and brush with olive oil.

   • Bake for 8–10 minutes, flipping halfway, until crisp and golden. Cool slightly.

4. Cook the Steak:

   • Heat a cast iron or heavy skillet over high heat.

   • Pat steak dry and season with salt and pepper.

   • Sear for 2–3 minutes per side for medium-rare, or to desired doneness.

   • Let rest 5–10 minutes, then slice thinly against the grain.

5. Assemble the Crostini:

   • Spread a layer of horseradish sauce onto each toasted bread slice.

   • Top with a spoonful of caramelized onions.

   • Add a slice or two of steak on top.

   • Garnish with herbs, shaved Parmesan, or a drizzle of balsamic glaze.

Tips, Variations & Substitutions

• Make Ahead: Caramelized onions and horseradish sauce can be made up to 3 days in advance and stored in the fridge.

• No Horseradish? Try garlic aioli, blue cheese spread, or Dijon mustard mayo.

• Vegetarian Option: Swap steak with sautéed mushrooms and add extra cheese.

• Cheese Twist: Spread a thin layer of goat cheese or whipped feta under the steak.

• Balsamic Finish: A light drizzle of balsamic glaze adds acidity and sweetness.

Hosting Tip: Lay out all components separately and assemble just before serving to keep the crostini crisp.

Serving Ideas & Occasions

These crostini are ideal for:

• Holiday parties

• Cocktail hours

• Dinner party starters

• Upscale game day snacks

Serve with:

• Sparkling wine or Champagne

• Bold red wines (Cabernet, Syrah)

• Classic Old Fashioned or bourbon-based cocktails

They also work well as part of a charcuterie board-inspired spread alongside cheeses, olives, and spreads.

Nutritional & Health Notes

While rich and indulgent, these steak crostini can fit into a balanced menu:

• Protein from steak supports satiety

• Healthy fats from olive oil and sour cream add flavor

• Portion control is built-in with small, individual servings

To make it lighter:

• Use whole grain baguette slices

• Swap sour cream for Greek yogurt

• Serve with a side of fresh greens or fruit skewers for balance

FAQs

Q1: Can I make steak crostini ahead of time?

A1: You can prep all the components ahead—caramelize the onions, mix the sauce, and cook the steak. Assemble just before serving for best texture.

Q2: What’s the best steak cut for crostini?

A2: Ribeye, sirloin, and filet mignon all work well. Choose a cut with good flavor and slice it thin against the grain.

Q3: Can I use jarred horseradish?

A3: Yes, prepared horseradish (refrigerated, not creamed) works great. Adjust amount based on your heat preference.

Q4: How do I keep crostini from getting soggy?

A4: Toast them well and cool completely before adding toppings. Spread the horseradish sauce right before serving.

Q5: What wine pairs best with steak crostini?

A5: Bold reds like Cabernet Sauvignon, Syrah, or Zinfandel. For whites, try a buttery Chardonnay.

Q6: Can I use store-bought caramelized onions?

A6: You can, but homemade has deeper flavor. If using store-bought, warm slightly and taste for seasoning.

Q7: How many crostini per person?

A7: For appetizers, plan 2–3 per guest. For a cocktail party with multiple dishes, 1–2 per guest is plenty.

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