Why is my mac 'n' cheese grainy? I need to make a large batch (to serve 30) of mac 'n' cheese, and rather than bothering with my standard roux - cheese sauce, I thought maybe I could cheat with a short cut.

I dug up an old recipe for crock pot mac 'n' cheese. I have used it with great success many times over, and never had it fail. I  thought I'd do a small "trial run" of it since it's been a while since I used it. Failure. I have a few theories on what may have gone wrong, but I'd love input from impartial cooks.

For what it's worth, the recipe calls for 4 cups cheddar, 1 cup jack, 2 cups milk, 2 cups cream, salt, pepper, dry mustard, few dashes hot sauce (optional), a pound of macaroni and a half cup of sour cream. Throw everything except macaroni and sour cream in crock, cover and cook on low for 1 hour. Stir in mac and sour cream, cover and cook for another hour to an hour and fifteen.

When I stirred in the macaroni, the sauce did look a bit "gloopy" but it wasn't really very warm yet, and If I recall correctly, that is how it always looks at this point.

I did use all milk instead of part milk/part cream, as I didn't have any cream on hand.
The problem is your putting all your cheese in at once. These cheese is going to settle on the bottom which would cause to clump up and be gloopy.

you need to stir small portions of the cheese at a time until it is melted. rinse, repeat and continue.

of course this is a crock pot recipe....

your probably best to make the cheese sauce portion on the stove first, then combine in a crock pot after.