Shred the cheddar and Monterey Jack cheese from a block and set aside. Bring it to room temperature for smoother melting.
In a high-walled pot, cook and crumble the ground beef over medium-high heat. Drain any excess grease and set the beef aside.
In the same pot, melt the butter and sauté the minced garlic for 1 minute until fragrant.
Add the taco seasoning, Worcestershire sauce, tomato paste, beef broth, chicken broth, milk, and Rotel tomatoes. Stir to combine and bring to a gentle boil.
Add the pasta shells to the pot, making sure they’re submerged in the liquid. Cover and cook according to the pasta package instructions, stirring halfway through to prevent sticking.
Once the pasta is tender, reduce the heat to low. Gradually stir in the cheese until melted and creamy.
Let the pasta sit for a few minutes to thicken, then serve and enjoy!