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A horizontal photo of a white platter filled with French Onion Crostini with melted cheese and thyme sprigs on top.
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5 from 4 votes


Everything you love about French onion soup is in these French Onion Crostini appetizers...except for the spoon.
Prep Time10 mins
Cook Time45 mins
Total Time55 mins
Course: appetizers, Appetizers and Snack Recipes
Servings: 16 servings
Calories: 138kcal


For the garlic toasts:

  • 1 baguette or long ciabatta sliced diagonally (into 1" slices)
  • 2 tablespoons olive oil
  • salt and pepper to taste
  • 3 cloves garlic

For the caramelized onions:

  • 3 large sweet onions sliced
  • 1 tablespoon olive oil
  • 2 tablespoons butter
  • ½ teaspoon salt
  • ¼ teaspoon black pepper
  • 4-5 sprige fresh thyme
  • 2 teaspoons granulated sugar
  • ¼ cup beef stock or broth
  • 5 ounces shredded Gruyere cheese
  • fresh thyme sprigs for garnish optional


To make the caramelized onions:

  • Peel and thinly slice 3 large sweet onions.
  • In a large skillet over medium heat, melt 2 tablespoons of butter along with 2 tablespoons of olive oil.
  • Add the sliced onions in an even layer to the skillet along with salt, pepper, and thyme sprigs.
  • Cook, stirring only occasionally, while the onions brown and caramelize for about 15 minutes.
  • Add 2 teaspoons sugar to the onions, stir, and add ¼ cup of beef broth (or stock). Stir and cook for an additional 5-10 minutes until deeply caramelized.
  • Remove the onions from the heat, and dispose of the thyme stems.
  • The caramelized onions are now ready to use or store in an air-tight container in the refrigerator.

To make the garlic toasts:

  • Preheat oven to 425-degrees Fahrenheit.
  • Use a serrated knife to slice the bread into 1" diagonal slices.
  • Place the slices on a parchment-lined baking sheet, brush them with olive oil, and season each with salt and pepper.
  • Bake in the preheated oven for 15 minutes until lightly golden.
  • Meanwhile, remove the skins from 2-3 garlic cloves.
  • When the toasts cooled, rub the raw garlic cloves lightly over each toasted crostini.

How to assemble the French onion crostini appetizers:

  • Once the onions are cooled, and the toasts have been rubbed with garlic, it's time to assemble the appetizers.
  • Spread approximately 1 tablespoon of the caramelized onions evenly onto each garlic toast.
  • Top each with some shredded Gruyere cheese and heat in a 350-degree (F) oven until the cheese has melted (approximately 10 minutes).
  • Before serving, top each with a small sprig of fresh thyme and serve warm or at room temperature.


The caramelized onions for this recipe may be made in advance and store in an air-tight container in the refrigerator for up to 3 days if needed.


Serving: 1serving | Calories: 138kcal | Carbohydrates: 13g | Protein: 5g | Fat: 8g | Saturated Fat: 3g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 3g | Trans Fat: 1g | Cholesterol: 14mg | Sodium: 223mg | Potassium: 110mg | Fiber: 1g | Sugar: 4g | Vitamin A: 140IU | Vitamin C: 4mg | Calcium: 117mg | Iron: 1mg