Black Bean and Corn Quesadillas

INGREDIENTS

• 2 teaspoons olive oil
• 3 tablespoons finely chopped onion
• 1 (15.5 ounce) can black beans, drained and rinsed
• 1 (10 ounce) can whole kernel corn, drained
• 1 tablespoon brown sugar
• 1/4 cup salsa
• 1/4 teaspoon red pepper flakes
• 2 tablespoons butter, divided
• 8 (8 inch) flour tortillas
• 1 1/2 cups shredded Monterey Jack cheese, divided