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Balsamic Caramelized Onion Crostini is a slightly spicy and highly flavorful appetizer.
5 from 8 votes

Balsamic Caramelized Onion Crostini

Balsamic Caramelized Onion Crostini is a slightly spicy and highly flavorful appetizer.  The topping is deep and rich in color and is also great on bean burgers!
Course Appetizer
Cuisine Finger Food
Prep Time 10 minutes
Cook Time 40 minutes
Total Time 50 minutes
Servings 36 Crostini
Calories 135kcal


  • 1 pound onions - diced small
  • 1 tablespoon extra virgin olive oil
  • 3 cloves garlic - finely chopped
  • 2 tablespoon cider vinegar
  • 3 tablespoon coconut sugar
  • 1 tablespoon balsamic vinegar
  • 2 teaspoons cornstarch
  • ¼ cup water
  • 1 teaspoon sriracha sauce - you can add more if you want it spicier but wait until it is all done and tested
  • ¼ teaspoon sea salt
  • teaspoon black pepper

For the Toasts:

  • 36 slices Italian bread - one long loaf
  • 3 tablespoons extra virgin olive oil


  • Heat oil in a large pot.
  • Add onions and saute for 20 minutes stirring frequently.
  • Add garlic and cook one more minute.
  • Add cider vinegar and coconut sugar.  Stir in and cook another minute.
  • Add balsamic vinegar and heat through.
  • Mix cornstarch with water and add to the pot.  Cook on low and stir and cook until thickened sauce. 
  • Stir in Sriracha, salt and pepper.  Taste and add more seasoning if you prefer.
  • Serve now, or refrigerate for later or freeze now. 

IF SERVING NOW - Prepare the crostini toasts:

  • Lay out the Italian bread slices on a cookie sheet. Lightly brush each bread with olive oil. The new silicone brushes are great. They wash up really easy.
  • Put the cookie sheet under broil. Don't do anything else. Just stand there and keep checking the bread and don't let burn. It only takes a couple of minutes.
  • After the toasts are lightly browned, remove from the oven. They are ready to use anytime.
  • Spread with Balsamic Caramelized Onion or serve Balsamic Caramelized Onion in a bowl with the toasted crostini on the side.
  • You can keep the toasts in the refrigerator for later use too. Like, if the party is tomorrow or in a few days.


Serving: 2Crostini | Calories: 135kcal | Carbohydrates: 12g | Protein: 1g | Fat: 8g | Saturated Fat: 4g | Sodium: 96mg | Potassium: 62mg | Sugar: 7g | Vitamin C: 1.1mg | Calcium: 3mg | Iron: 0.5mg