Roll out the dough on a lightly floured surface until it forms a 14-inch circle. Carefully transfer the dough to a 9-inch springform pan, pressing it firmly against the bottom and sides. Refrigerate the crust while you prepare the filling.

Cook the bacon in a large skillet over medium heat until it becomes crisp, stirring occasionally. Use a slotted spoon to remove the bacon and drain it on paper towels. Reserve 1 tablespoon of the bacon drippings in the pan and discard the rest. Add the onions to the reserved drippings and cook over medium heat, stirring frequently, until they are caramelized, which should take about 20-25 minutes.

Once the onions are caramelized, stir in the thyme, pepper, and nutmeg, then remove the pan from the heat. Allow the onion mixture to cool slightly before stirring in the cheese and reserved bacon. Spoon this filling into the chilled crust.

Preheat your oven to 350°F. In a large bowl, whisk together the eggs, milk, and cream until well blended. Pour this mixture over the filling in the crust. Place the springform pan on a rimmed baking sheet to catch any potential spills.

Bake the quiche on a lower oven rack for 75-85 minutes or until a knife inserted near the center comes out clean. Allow the quiche to cool on a wire rack for 15 minutes before running a knife around the inside of the pan to loosen the sides. Finally, remove the rim of the springform pan and serve the quiche warm or at room temperature.