Cook the 16 oz elbow macaroni according to package instructions until al dente. Drain and set aside.
In the crockpot, add the cooked macaroni, cubed 1/2 cup butter, 12 ounces evaporated milk, 1 cup whole milk, 1/2 teaspoon salt, 1/4 teaspoon black pepper, 1/4 teaspoon garlic powder, 1/4 teaspoon onion powder, 1/4 teaspoon paprika, 1/4 teaspoon mustard powder and 1/4 teaspoon cayenne pepper(if using). Stir to combine.
Add the cubed 1 pound Velveeta cheese and 2 cups shredded sharp cheddar cheese to the crockpot.
Cover and cook on low for 2-3 hours or on high for 1-2 hours, stirring occasionally, until the cheeses are melted and the mixture is creamy and smooth.
Once the macaroni and cheese is heated through and creamy, adjust the seasoning with additional salt and pepper if needed.
Serve the crockpot Velveeta macaroni and cheese hot, garnished with Chopped parsley or chives if desired.