In a large skillet over medium-high heat, cook the ground beef with the taco seasoning until browned and fully cooked.
Add the tomato sauce and salsa and stir until combined.
Add the uncooked shell pasta, beef broth, and milk. Mix well.
Bring to a simmer, reduce the heat to low, cover, and cook about 10 minutes, stirring occasionally, until the pasta is tender. Add a splash more broth or milk if it needs longer.
Stir in 1 1/4 cups of the Mexican cheese until melted.
Sprinkle the remaining 1/4 cup cheese over the top, cover, and let it melt.
