01 - Heat olive oil in a large skillet over medium heat. Add chopped onion and cook until softened, about 2–3 minutes.
02 - Stir in minced garlic and cook for 30 seconds until aromatic.
03 - Add ground beef, breaking it up with a spoon. Cook until browned and fully cooked, approximately 5–7 minutes.
04 - Incorporate cumin, chili powder, smoked paprika, salt, and black pepper. Cook for an additional minute, then remove from heat.
05 - Place one tortilla flat. Layer half with cheddar and Monterey Jack cheeses, then add beef mixture and sprinkle with cilantro if using. Fold tortilla in half. Repeat with remaining tortillas.
06 - Heat a nonstick skillet or griddle over medium heat. Melt butter, then cook each quesadilla for 2–3 minutes per side until golden and cheese is melted.
07 - Transfer cooked quesadillas to a cutting board. Allow to rest for 1 minute, then slice into wedges.
08 - Present warm with salsa, sour cream, and guacamole as accompaniments.