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French Onion Crostinis

These delicious crostinis are topped with perfectly caramelized onions, gruyere, and mozzarella to make a delicious appetizer!
5 from 2 votes
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Prep Time 10 minutes
Cook Time 1 hour
Total Time 1 hour 10 minutes
Course Appetizer

Ingredients
  

For caramelized onions

  • 3 sweet onions halved, thinly sliced
  • 2 teaspoon butter
  • 2 teaspoon olive oil
  • 1 teaspoon dried thyme
  • pinch of salt

For crostinis

  • 1 baguette
  • 2-3 tablespoon olive oil
  • pinch of salt

For topping

  • ⅔ cup gruyere cheese shredded
  • ⅔ cup mozzarella cheese shredded
  • optional for garnish: fresh thyme sprigs

Instructions
 

For caramelized onions

  • Heat olive oil and butter in a large skillet on medium heat.
  • Add sliced onions and dried thyme and cook, stirring frequently, until softened (about 5 min). Then, add pinch of salt.
  • Reduce heat to medium-low and stir every few minutes. It takes about 50-60 minutes for the onions to completely caramelize.

For crostinis

  • Preheat oven to 425F.
  • Slice baguette diagonally into about ½" thick pieces.
  • Brush each side with olive oil and sprinkle with salt.
  • Bake until crispy and golden, about 5-8 minutes.

Assembly

  • Top crostini with heaping spoonful of caramelized onion.
  • Evenly distribute mozzarella and gruyere on top of the crostinis.
  • Broil for 3-5 minutes, until cheese is melted and slightly browned.
  • Remove from heat and garnish each crostini with sprig of fresh thyme.
Keyword vegetarian
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