Cook the PastaCook elbow pasta according to package instructions until al dente. Drain and set aside.
Melt the Cheese MixtureIn a skillet, melt butter, cheddar cheese, and mozzarella cheese. Stir until smooth.
Assemble in the CrockpotAdd the cheese mixture, cheddar cheese soup, and sour cream to the crockpot. Stir to combine.
Add Remaining IngredientsAdd the cooked pasta, milk, mustard powder, salt, and paprika. Stir everything together.
CookCover and cook on low for 2 hours, stirring occasionally.
ServeServe hot and enjoy creamy, cheesy perfection!