01 - Heat olive oil in a skillet over medium heat. Add onions and cook until softened, about 2 minutes. Add garlic and sauté for 30 seconds until fragrant.
02 - Add ground beef and cook, breaking it up with a spoon, until browned, about 5 minutes. Stir in taco seasoning, salt, pepper, tomato paste, and water. Simmer for 2-3 minutes until thickened. Remove from heat.
03 - Warm tortillas in a dry skillet for 30 seconds per side or in the microwave for 20 seconds until pliable.
04 - Lay each tortilla flat. In the center, layer one-fourth of the rice, beef mixture, black beans, tomato, salsa, sour cream, and a mix of both cheeses. Sprinkle with cilantro if desired.
05 - Fold in the sides and roll up tightly from the bottom to form secure burritos, ensuring the filling is completely enclosed.
06 - Spread a thin layer of softened butter evenly over the outside surface of each burrito.
07 - Heat a large skillet or griddle over medium heat. Place burritos seam-side down and grill for 2-3 minutes per side, pressing gently with a spatula, until tortillas are golden brown and cheese is melted.
08 - Slice each burrito in half diagonally and serve immediately while hot and crispy.