Start of by boiling your macaroni in a saucepan until al dente, about 6 minutes. Drain.
In a separate saucepan, combine the butter and cheese and the cream cheese. Stir until incorporated.
Next, in your Crock pot, combine cheese/cream cheese/butter mixture and add in the beaten eggs, sour cream, soup, salt, milk, mustard and pepper and combine well.
Add in your drained macaroni and stir again until its all completely covered
Cook on LOW setting for 2.5 to 3 hours, stirring periodically.