French Onion Crostini

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

**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.

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

• baguette or ciabatta lunga (long ciabatta, shown)
• olive oil
• raw garlic cloves
• sweet onions (2-3)
• salt an pepper
• fresh thyme sprigs
• granulated sugar
• beef stock or broth
• shredded Gruyere cheese

Kitchen tools and equipment needed:

• baking sheets
• parchment paper
• serrated knife
• chef's knife or santoku (shown)
• cutting board
• large skillet (cast iron shown)
• slotted spatula
• measuring cups and spoons
• cheese shredder/grater

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.

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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.

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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.

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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. 

*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! 🙂

*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!!

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.

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Printable Recipe Card

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!