Heat a large skillet over medium-high heat for about 2 minutes. Add the lean ground beef, breaking it up with a spatula as it cooks. Stir continuously for 5-7 minutes until browned and no longer pink. Drain excess grease.

Reduce the heat to low and stir in tomato paste, beef broth, and taco seasoning. Allow the mixture to simmer for 2-3 minutes, stirring occasionally until sauce thickens.

Clean the skillet and return it to medium-low heat. Brush with vegetable oil or butter. Place a tortilla in the skillet, sprinkle with cheddar cheese, add beef mixture, and top with Monterey Jack cheese.

Fold the tortilla in half and cook for 2-3 minutes on each side until golden brown and cheese is melted. Flip and cook until the other side is equally crispy.

Transfer to a cutting board, let rest for 1 minute, and slice into triangles. Garnish with cilantro and serve with sour cream.