Sweet onion pie

3 tablespoons unsalted butter
4 large Vidalia onions, cut in half, then thinly and uniformly sliced on a mandoline
1 partially baked 9-inch pastry shell and when cool, rubbed with cold butter
1 cup grated Gruyère cheese
2 large eggs
2 large egg yolks
1 1/2 cups of half and half
1 teaspoon salt
Plenty of white pepper

Preheat the oven to 350°F.

Melt 3 tablespoons butter in a heavy saucepan.  Add onions and cook over medium-low heat, tuning regularly until clear and limp but not brown. Drain the onions and arrange them in a cold pastry shell.  Cover the onions with the grated cheese.  Beat the eggs yolks, eggs and half and half together and pour over cheese and onions. Season with salt and white. pepper.

Bake until the pie is golden brown all over about 40 minutes.