We do not recommend preparing the augratin potatoes in a slow cooker. The slow cooking temp and the long cooking time do not work well with dairy product, they tend to separate and curdle. You can prepare in the oven and keep warm in the slow cooker - great idea.
I have a recipe for preparing 3 boxes of Augratin at a time if that will help you.
Oven Directions for 15 Servings: Make as directed for 5 Servings—except use 4-quart casserole, 7 cups boiling water, 1 1/2 cups milk, 6 tablespoons margarine or butter, 3 packets Au Gratin Sauce Mix and 3 pouches Potatoes. Bake about 35 minutes.
Answered 12/21/2012 by Betty Kitchen Expert