Put your water on to boil and cook your noodles till al dente. (this means not all the way cooked still a little firm)
Place the wet ingredients into your slow cooker first.
Then whisk in the Ground Mustard, salt and pepper.
Scatter your butter slices around the slowcooker.
Throw in your cheeses.
Drain your pasta and stir into the cheese mixture.
Put the lid on and cook on low for 2 1/2 hours.
DO NOT let your slow cooker sit on warm when itâ??s done or it will over cook and burn your Mac and Cheese.