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French Onion Crostini

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Everything you love about French onion soup is in these French Onion Crostini…except for the spoon.

A vertical closeup of a platter of French Onion Crostini along with melted cheese, fresh thyme, with  onions and garlic in the background.

**Please Note – The printable recipe card with detailed instructions, complete ingredient measurements, and nutritional information for making these savory caramelized onion crostini is available at the end of this post. OR you can hit the “jump to recipe” button (found above) to be taken directly to the recipe.

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An overhead vertical photo of a tray filled with French Onion Crostini along with onions and garlic in the background.

The ingredient list:

**Note – The following lists of ingredients plus kitchen tools and equipment contain affiliate links (highlighted in blue) for your consideration and shopping convenience. #CommissionsEarned

Kitchen tools and equipment needed:

Why this recipe works:

French Onion Bruschetta is really easy to make and everyone loves them.

They can be served for any occasion from extremely fancy (think wedding or cocktail party) to extremely casual (think game day or tailgating).

These 2-3 bite appetizers can be eaten standing up or sitting down, and with only one hand, leaving the other hand free for sipping on your favorite beverage.

They are lightly sweet and nicely crunchy with the mildest hint of garlic.

They also have a lovely nutty flavor that the topping of Gruyere cheese provides, and the fresh thyme adds the unmistakable flavor you know and love about French onion soup.

How long do these tasty appetizers take to make?

Well, that depends on if you make the caramelized onions ahead of time, or if you make them the same day as you make the French onion crostini appetizers.

If you make the caramelized onions ahead of time, you can store them in the refrigerator for up to 3 days before you assemble the appetizers.

All total, if you make the onions and assemble the crostini on the same day, these French onion garlic toasts will take 2about 1 hour to make from start to finish.

How long does it take to caramelized onions?

In order to properly caramelize onions and develop their sweet, nutty flavor, it will take at least 25 minutes over medium heat in a large skillet.

Can these caramelized onion crostini appetizers be made and assembled in advance?

Yes, but I wouldn’t make and assemble them too far in advance.

Maybe only like 4-5 hours and then store them loosely covered in the refrigerator until ready to reheat.

How to reheat French onion crostini:

Preheat the oven to 350-degrees.

Place the assembled French onion crostini on a parchment-lined baking sheet and reheat in the oven for 7-10 minutes or until hot.

Can another cheese be substituted for the Gruyere in this recipe?

Honestly, if possible, I’d like you to stick with the Gruyere for the best possible flavor.

However, shredded Swiss cheese will work in a pinch, and still give you that great French onion soup flavor you know and love.

Can dried thyme be substituted for fresh thyme for these appetizers?

Yes, but be cautious not to use too much.

Dried herbs are more intense in flavor so if using dried thyme over fresh, please use it sparingly.

Say good bye to boring bread. Did you know French onion crostini can also be served as a side to soup and stews?

Here are some soup and stew recipes you’re going to love.

Spaghetti Squash Soup, Stuffed Green Pepper Stew, Beef Stew for a Crowd, Instant Pot Italian Pepperoni Soup, Chicken Noodle Soup with Leeks and Kale, German Onion Soup with Bratwurst…just to name a few. 🙂

The step-by-step photo instructions for making French Onion Crostini:

How to prepare the caramelized onions:

*Note – These can be prepared in advance and kept in an air-tight container in the refrigerator for up to 3 days if needed.

  • Peel and thinly slice 3 large sweet onions.
  • In a large skillet over medium heat, melt 2 tablespoons 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.

How to prepare the garlic toasts:

  • Preheat oven to 425-degrees Fahrenheit.
  • Use a serrated knife to slice the bread into 1″ diagional 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 removed from the oven and 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.
A closeup horizontal photo of melted cheese and fresh thyme sprigs on some French Onion Crostini appetizers.

Additional recipes featuring French caramelized onions:

*French Onion Pork Chops (shown below and featured in the video)

All the flavors you love in a traditional French onion soup are captured in this recipe for French Onion Pork Chops. 

Two cheesy French onion pork chops on a blue scalloped plate

*French Onion Stuffed Shells (not shown)

Everything you love about French onion soup is in these French Onion Stuffed Shells, but now it’s in a brand new (yet still incredibly delicious, and cheesy) unexpected form.

*French Onion Mac and Cheese (shown below)

Today’s French Onion Mac and Cheese recipe has got your name written ALL over it, and I’m happily handing it to you! You’re welcome! 🙂

A horizontal photo of French Onion Mac and Cheese in a casserole dish with a spoon and two onions in the forefront.

*French Onion Sloppy Joes (not shown)

When you want to frugally feed a crowd for game day, or a hungry family at dinner, it doesn’t get much tastier than French Onion Sloppy Joes!

*French Onion Crostini Appetizers (shown below) THIS IS THE PLACE!!

A vertical two image collage along with a title text overlay graphic for French Onion Crostini with melted cheese and fresh thyme.

Below is the printable recipe card along with the exact ingredient measurements and nutritional information for making today’s easy caramelized onion French onion appetizer recipe.

If you’ve made this recipe, or are excited to make this recipe, I’d appreciate it if you’d take a moment to leave it a star rating in the recipe card, along with a comment if you’re so inclined. Thank you. 🙂

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

FRENCH ONION CROSTINI

Renee – Kudos Kitchen
Everything you love about French onion soup is in these French Onion Crostini appetizers…except for the spoon.
5 from 3 votes
Prep Time 10 mins
Cook Time 45 mins
Total Time 55 mins
Course appetizers, Appetizers and Snack Recipes
Servings 16 servings
Calories 138 kcal

Ingredients
  

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

Instructions
 

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.

Notes

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.

Nutrition

Serving: 1servingCalories: 138kcalCarbohydrates: 13gProtein: 5gFat: 8gSaturated Fat: 3gPolyunsaturated Fat: 1gMonounsaturated Fat: 3gTrans Fat: 1gCholesterol: 14mgSodium: 223mgPotassium: 110mgFiber: 1gSugar: 4gVitamin A: 140IUVitamin C: 4mgCalcium: 117mgIron: 1mg
Keyword Caramelized onion appetizer toasts, Frenc onion appetizers, French onion Bruschetta, French onion crostini, French onion garli toasts
Tried this recipe?Let us know how it was!

Thank you so much for visiting me here today in my Kudos Kitchen!

I sincerely hope you’ve enjoyed today’s caramelized onion appetizer recipe for French Onion Crostini as much as I’ve enjoyed (eating) and bringing it to you!

A closeup photo of French Onion Crostini on a plate with melted cheese and fresh thyme sprigs on top.

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Recipe Rating




Jill Baird

Friday 27th of August 2021

This looks incredible and is the perfect addition to a cozy fall soup. I think I'll add it to our weekend menu of roasted tomato soup. Delicious! I can't wait to try it! Thanks for all the great recipes!

Renée

Monday 30th of August 2021

I think that's a smart idea, Jill. I know you'll love these with your soup. Enjoy! -Renee

Gina

Friday 27th of August 2021

Love how this turns my favorite soup into an appetizer! Those caramelized onions are to die for!

Renée

Monday 30th of August 2021

What could be better? Enjoy them, Gina!! Take good care, Renee