The Best Brussels Sprouts & Caramelized Onion Vegetarian Quesadillas

It has been snowing for weeks, so I’ve been making comfort food like these vegetarian quesadillas like crazy. I can eat quesadillas for breakfast, lunch, and dinner, but the combination of earthy Brussels sprouts and sweet caramelized onions truly makes these the best I’ve ever had. They are topped with a super spicy and creamy serrano pepper and cilantro sauce.

Overhead shot of vegetarian quesadilla cut into quarters and sprinkled with serrano sauce, queso fresco, and cilantro

How do you Caramelize Onions?

A lot of people feel intimidated when they hear that caramelizing onions can take up to an hour but, other than the time investment, there’s really not much to it.

Here are some tips to make the process as painless as possible:

  • Start with a combination of butter and vegetable oil: I find it really hard not to burn butter because it has such a low smoking point, so I like to mix it with some vegetable oil to prevent this from happening. You will still get the richness from the butter but without any funky burnt flavors.

Overhead shot of caramelized onions in a stainless steel pan

  • Use a little bit of water to help things along: if you notice that the onions are starting to look burnt but you’ve only been cooking them for 15 min, add a tablespoon of water to your pan and scrape up all the brown bits at the bottom. You can do this as many times as you need to.
  • Deglaze the pan at the end with booze: Deglazing means to add a liquid so that you can scoop up all the flavorful bits that are stuck to the pan. Water will do just fine, but deglazing with some white wine or beer will really take your caramelized onions to the next level.

What are the Best Tortillas for Making Vegetarian Quesadillas?

I strongly believe that you should only make quesadillas out of flour tortillas because they crisp better.

I also like to buy the ones for “soft tacos” at the store because they tend to be a more manageable size than bigger ones. You will have to flip them, so I recommend buying 10-inch tortillas.

Overhead shot of flour tortilla in a pan topped with cheese and caramlized onions

Other Ideas for Toppings

I topped these vegetarian quesadillas with queso fresco (a soft Mexican cheese), some serrano-cilantro sauce, and a bit of chopped cilantro.

They would also be great topped with some sliced avocado and chopped green onions or with a dollop of sour cream to balance out the heat of the serrano sauce.

Close up of stacked vegetarian quesadillas
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The Best Brussels Sprouts & Caramelized Onion Vegetarian Quesadillas

These vegetarian quesadillas pack a ton of flavor and are perfect for breakfast, lunch, dinner, or as an appetizer for a party.
5 from 5 votes
Prep Time: 15 minutes
Cook Time: 1 hour
Total Time: 1 hour 15 minutes
Course: Appetizer
Cuisine: Mexican American
Keyword: caramelized onions, easy appetizer, easy dinner, vegetarian, vegetarian appetizers
Servings: 1
Calories: 2221kcal
Author: Daniela Miranda


For the Quesadillas

  • 2 10-inch flour tortillas (you can also use gluten-free tortillas)
  • 1 cup Pepperjack cheese grated
  • 2 tbsp caramelized onions (recipe follows)
  • 2 cups Brussels sprouts shredded or thinly sliced
  • 3 tbsp vegetable oil divided

For the Caramelized Onions

  • 1 tbsp vegetable oil
  • 1 tbsp butter
  • 1 large yellow onion cut in half and thinly sliced
  • 1/4 cup white wine optional
  • kosher salt
  • pepper freshly ground

For the Serrano-Cilantro Sauce

  • 5 serrano peppers stemmed and coarsely chopped
  • 1 bunch cilantro coarsely chopped
  • 1 small garlic clove coarsely chopped
  • 1 lime juiced
  • 1/2 cup sour cream
  • 1/4 cup mayonnaise
  • 2 tbsp vegetable oil
  • Kosher salt


  • queso fresco
  • chopped cilantro
  • avocado


To make the caramelized onions

  • Set a 12-inch stainless steel pan over medium high heat and add the vegetable oil and butter.
  • Add the onions and cook for 40-60 min or until the onions are a deep brown color. If the onions look dry or start to burn add a tablespoon of water to the pan and scrape up all the bits that are stuck to the bottom.
  • Five minutes before the onions are ready, add wine to the pan and scrape up all the brown bits stuck to the bottom (this step is optional).
  • Transfer the onions to a bowl and set aside.

To make the serrano-cilantro sauce

  • Add all of the ingredients to the bowl of a food processor and process until smooth. Add salt and pepper to taste and set aside.

To assemble the quesadillas

  • Add two tablespoons of vegetable oil to the same pan you used to caramelize the onions. Heat the oil over medium high heat. When the oil is hot, add the Brussels sprouts and cook for 3-5 min until soft. Set aside.
  • Heat a 12-inch non-stick skillet over medium heat. Add one tablespoon of vegetable oil to the pan.
  • Take one tortilla and place it in the hot pan.  Sprinkle it with a third of the Pepperjack cheese. Top the cheese with two heaping tablespoons of the caramelized onions and half a cup of the Brussels sprouts. Top with the rest of the cheese and place the other tortilla on top. Cook for 5 min or until the bottom tortilla starts to brown.
  • Push down on the quesadilla with a spatula or flipper. Carefully flip the quesadilla and cook on the other side for 5 min or until browned.
  • Remove the quesadilla and place it on a cutting board. Cut into quarters and transfer to a plate. Top with serrano-cilantro sauce and any other toppings you choose. Serve immediately.


  • You will have leftover caramelized onions and Brussels sprouts to make another quesadilla. They will both keep in the fridge for 3 days.


Calories: 2221kcal | Carbohydrates: 75g | Protein: 44g | Fat: 196g | Saturated Fat: 115g | Cholesterol: 214mg | Sodium: 1627mg | Potassium: 1478mg | Fiber: 13g | Sugar: 20g | Vitamin A: 4090IU | Vitamin C: 197.1mg | Calcium: 1154mg | Iron: 6.4mg

Here are other spicy recipes you might enjoy:

If you like this recipe, please make sure to pin it, share it on social media, or email it to your friends. Don’t be shy! People are always grateful for some cooking inspiration 🙂

Also, if you have any questions or just want to let me know that you liked the recipe, please leave a comment below. Hearing from other adventurous home cooks always makes my day!

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