Heat a large skillet over medium-high heat and add the ground beef. Break it apart with a wooden spoon, cooking until finely crumbled and deeply browned (about 5-7 minutes). Drain any excess grease.

Stir in the taco seasoning, tomato paste, and beef broth. Reduce the heat to low and simmer for 2-3 minutes until the beef is coated in a thick, light reddish-brown tomato paste sauce.

Wipe the skillet clean and return it to medium-low heat, brushing lightly with vegetable oil. Lay a tortilla flat in the pan. Sprinkle a thick bottom layer of cheddar cheese over one half, add an even middle layer of the beef mixture, and top with the Monterey Jack cheese.

Fold the empty half of the tortilla over the filling, pressing gently. Cook for 2-3 minutes until the bottom has golden-brown, slightly blistered crispy spots. Carefully flip and cook for an additional 2 minutes on the other side.

Transfer the quesadilla to a cutting board and let rest for 1 minute. Slice into three triangles. Plate on a matte grey ceramic plate, garnish with scattered chopped cilantro, and serve with a ramekin of sour cream.