1. Cook the ground beef in a skillet over medium heat until browned, then add the onion and cook until softened.

2. Stir in the garlic, tomato paste, taco seasoning, salt, and black pepper, then cook until the mixture is well combined and thickened slightly.

3. Lay the tortillas flat and add cheddar cheese, beef filling, and Monterey Jack cheese to one half of each tortilla.

4. Fold the tortillas over and cook them in a lightly oiled skillet until golden brown on the first side.

5. Flip and cook the second side until crisp and the cheese is fully melted.

6. Let the quesadillas rest briefly, then slice and serve with sour cream and parsley.