In a large skillet, heat a splash of oil over medium heat. Add the ground beef and cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain any excess fat, then stir in the tomato paste and any seasonings of your choice. Cook for another 2-3 minutes until everything is well combined and heated through.

Warm your flour tortillas briefly in a dry skillet or microwave to make them pliable. Place one tortilla on a clean surface and sprinkle a layer of sharp cheddar cheese on one half. Top the cheese with a generous scoop of the seasoned ground beef mixture, followed by a sprinkle of Monterey Jack cheese. Fold the tortilla over to create a half-moon shape.

In the same skillet over medium-low heat, add the folded quesadilla and cook for about 2-3 minutes, or until the bottom is golden brown and crispy. Carefully flip the quesadilla using a wide spatula and cook the other side for an additional 2-3 minutes, ensuring the cheese melts and the tortilla is evenly browned.

Once both sides are deliciously golden and crispy, gently transfer the quesadilla to a cutting board. Allow it to rest for a minute before cutting it into wedges. Garnish with fresh cilantro if desired, and serve warm with a side of sour cream for dipping. Enjoy your homemade Ground Beef Quesadillas!