Boil the macaroni in water for six minutes and drain.
In the microwave, melt the butter.
Spray your slow cooker with non-stick cooking spray.* Combine melted butter, cheese, sour cream, soup, salt, milk, mustard and pepper in your slow cooker. Add the drained macaroni and stir again.
Cook on low for 2 to 2½ hours, stirring occasionally.**
Slightly adapted from: Six Sisters’ Stuff *If you prefer more of an oven-baked quality to the finished dish (i.e. some crispy bits and browning), I skip the spray. It will require a bit more scrubbing when you’re cleaning your crockpot, but I don’t mind.**Two hours is usually the perfect amount, but a little extra time never hurts it. I usually stir twice -- once after 45 minutes and again after an hour -- but I’ve also forgotten to stir it and it turns out just fine.