Boil water in a large pot; season with salt. Cook the elbow macaroni for 6-8 minutes until al dente; drain and set aside.
In a mixing bowl, combine the milk, heavy cream, and melted butter. Whisk in garlic powder, onion powder, paprika, salt, and pepper.
Add cooked macaroni into the crockpot. Pour the cheese sauce mixture over the pasta. Stir in the cheeses (cheddar, mozzarella, and Parmesan).
Set the crockpot to low heat for 2-3 hours, stirring occasionally. Cook until the cheese is melted and the mixture is creamy.
Stir well before serving; adjust seasoning as desired.
Notes
Use freshly shredded cheese for better meltability. Stir halfway through for even melting. For extra creaminess, add a splash of cream or milk just before serving. Garnish with breadcrumbs or herbs.