Jacques (Cooking at Home, pg 156) says 4c mashed potatoes, 3 eggs, 2/3 c Gruyere/Swiss, 1/4 tsp salt, 1/8 tsp pepper, mix, bake in a casserole dish at 400 for 30-35 min (pardon, Jacques, for my paraphrasing). I've made this often (often mashing potatoes to do it) and everyone loves it. It's very forgiving, if I have fewer eggs it turns out ok, and different types of cheeses (you want something fairly strong and a little firm/dry) in different amounts work well. I've been known to add a pinch of baking powder to give it more pouf, and you can season it more if you like. Great dish for banquets, buffets, potlucks.