01 - In a mixing bowl, blend pulled pork, barbecue sauce, chopped onion, cheddar, and Monterey Jack cheese until evenly coated.
02 - Lay out tortillas flat; evenly distribute filling over four tortillas, leaving a 1/2-inch border at the edges.
03 - Place remaining tortillas on top of filled tortillas, pressing gently to enclose the filling.
04 - Warm a large nonstick skillet over medium heat and melt 1/2 tablespoon butter.
05 - Carefully place quesadilla in skillet; cook 2–3 minutes per side until golden brown and cheese melts, replenishing butter as needed. Repeat for remaining quesadillas.
06 - Cut toasted quesadillas into wedges. Serve warm with sour cream, salsa, and chopped cilantro as desired.