Real cheddar, while delicious, is terrible for melting. Though I knew this, I thought maybe by adding Colby Jack cheese, milk, and butter in a crock pot that it would change. Nope. I was wrong. Very, very wrong. My mac and cheese was tasty, but looked terrible. The cheddar definitely separated. It just so happened that a friend came over for dinner. He was a good sport and even took some for lunch the next day.
Looks not so promising.
Also, don't set the Crockpot to high.