Here's mine, from the Anna Thomas Vegetarian Epicure - 1972. Granted it's not low-fat, but it's by far the best one I've ever made...would love to get other ideas from you!
Basic shortcrust pastry for one 10-inch pie
10 oz. Cheese (half Swiss and half Switzerland Gruyère, or in proportion desired) - my note: I use more than this more like 1 lb., 2/3 gruyere, 1/3 Emmenthaller)
2 Tbs. flour
2 large onions
4 Tbs. butter
1 tsp. chopped basil
1 large, firm tomato, sliced
2 large eggs
¼ cup cream
Prepare a shortcrust pastry for a 10-inch pie dish and chill it.
Grate all the cheese and toss it with the flour.
Melt the butter in a large skillet. Slice the onions and sauté them very gently in the butter until they begin to turn golden, about ½ hour. Spread about 1/3 of the cheese over the bottom of the pie dish then spread the onions over it. In the butter that is left in the pan, heat the tomato slices with the chopped basil for a minute or two. Arrange the tomato slices over the onions and cover with the remaining cheese.
Beat the eggs with the cream and pour it over the cheese. If you like nutmeg, sprinkle a little on top. Bake in a pre-heated, 350-degree oven for about 35 to 40 minutes until the top browns nicely. Serve hot, in wedges.