Stir in the crock pot:
Add more milk if needed to cover the pasta. Cook on high for 45 minutes.
Stir once while cooking, to prevent the pasta at the top from becoming dry and crispy.
The pasta should be beginning to soften, but not so soft that stirring smushes it.
Stir well. Reduce the temperature to low. Cook for about 90 minutes, until center does not jiggle and pasta is tender. Stir once more while cooking.
Serve promptly! Refrigerate any leftovers promptly! You will get macaroni and cheese soup if you leave it in the crock pot after it is done.