Preheat the oven to 350 degrees.If using a 9 inch springform pan, on a floured surface roll out your pie dough to about 14 inches. Transfer to your pan and press firmly against the sides and bottom. You can refrigerate or stick in the freezer while you are preparing the filling. Cook your bacon in a skillet until done and starts to crisp. With a slotted spoon, remove the bacon from the skillet and drain on a paper towel.
Remove all the bacon drippings from the skillet, reserving hopefully, except for a couple of tablespoons left in the pan. Add the butter and allow it to melt.
Add the onions and cook them, stirring occasionally until they are lightly caramelized. This may take 20-30 minutes. If there is excess fat, I pour that off and then add the thyme, the salt and pepper, the nutmeg.
Remove from the heat and allow to cool. Stir in the bacon and cheeses and spoon into the crust.
In a large bowl whisk the eggs, milk and cream. Place the springform pan on a sheet pan. Pour the egg mixture over the top.
Place in the oven and bake until a knife inserted in the center comes out clean. Depending on your oven start checking doneness after about 45 minutes by touching the middle. If it's firm to the touch it is done. You don't want to overcook. Ejoy!