Cook pasta for 2 minutes less than package recommendations so the pasta is still somewhat hard.
Drain the pasta reserving two cups, and dump pasta into a crock pot lined with a crock pot liner. Stir in butter to keep pasta from sticking to each other.
Stir in diced onion, if you are adding diced onions.
Add the shredded cheese, Velveeta, Alfredo sauce, sour cream, and milk over pasta. Stir to combine.
Season with onion powder, dry mustard, paprika, salt and pepper. Stir to combine.