• Lightly grease a 9-in (23 cm) springform pan with 3-in (7.5 cm) sides. Set aside.

PREPARE THE CRUST

• Make the two batches of Foolproof Shortcrust Pastry, one after the other.

  When the first one is done, dump it on a floured working surface, and make the second batch right away. Dump it over the first batch, then, using your hands, gather the whole thing into a loose, flattened ball. Sprinkle the dough with flour, then roll out to a 16-in (40 cm) circle. (Sprinkle with more flour as needed to prevent sticking.) The pastry should be about ¼ inch (6 mm) thick.
• Carefully fold the dough in half, then drape it over one half of the prepared springform pan. Unfold it, then gently ease the dough into the pan, pressing it onto the bottom and creasing the dough to flatten it against the sides of the pan. Using a fork, prick the bottom pastry all over.
• If blind baking with pie weights or dry peas, cut off the overhanging pastry so the pastry is flush with the top of the pan.

  If blind baking without pie weights or dry peas, let the pastry hang over the sides of the pan. Freeze the pastry-lined pan for at least 30 minutes, or until ready to blind bake.

BLIND-BAKE THE CRUST

• If blind baking with pie weights or dry peas, preheat the oven to 400°F (200°C). Cut out a large piece of parchment paper and ease it into the pastry to line it. Fill the pan with pie weights or dry peas. Bake for 30 minutes, then remove from the oven. Carefully lift the parchment with the weights or peas out of the pan (transfer these into a large bowl to let cool completely before storing), then lower the oven temperature to 350°F (175°C) and return the pan to the oven. Bake the crust for an additional 15 minutes, or until it looks dry and light golden brown. Set aside on a cooling rack.
• If blind baking without pie weights or dry peas, preheat the oven to 350°F (175°C). Transfer the pan with the overhanging pastry straight from the freezer to the oven. Bake for 45 minutes, or until the crust looks dry and is light golden brown. Set aside on a cooling rack.

PREPARE THE FILLING

• Cook the bacon: Arrange the bacon slices on a lined baking sheet and bake in a 400°F (200°C) oven until crisp. Transfer to paper towels to drain off the excess fat, then let cool completely. Once cooled, cut into strips and set aside.
• Cook the onions: Set a large saute pan or Dutch oven over medium heat, then add the olive oil and heat until shimmering. Add the sliced onions, sprinkle with 1 tsp (5 ml) of the salt, then stir to combine. Cover and cook for 15 minutes. Uncover, stir, reduce the heat to low, and continue cooking, uncovered, until the onions are tender and lightly browned, 15 to 25 minutes more. Stir every 5 minutes to ensure the onions cook evenly. Transfer the cooked onions to a large bowl and let cool completely.
• Make the custard: In a large bowl or an 8-cup measuring cup, combine the milk, cream, eggs, remaining salt, pepper, and nutmeg and, using a hand mixer, blend until very frothy (you can add the ingredients to a stand blender instead.)

BAKE THE QUICHE LORRAINE

• Preheat the oven to 325°F (160°C).
• Place the springform pan with the blind-baked crust on a rimmed baking sheet to catch any leaks. Combine the cooked onions and bacon, then spread a third of this mixture over the bottom of the crust. Pour a third of the custard over top, then sprinkle with a third of the grated cheese. Blend the remaining custard again to make it frothy, then repeat these layers twice more, ending with the cheese.
• Bake for about 90 minutes, or until the top of the quiche is golden brown and the edges are set, while the center still has a slight jiggle. The quiche will fully set as it cools.
• Transfer the Quiche Lorraine to a wire rack and let cool to room temperature, at least 2 hours.

  If you blind-baked the crust without pie weights or dry peas, use a sharp knife to trim the excess crust along the rim.

  Refrigerate until the quiche is fully chilled, at least 2 more hours, or ideally overnight. Refrigerating the quiche will allow it to fully set and slice more cleanly. You can keep the quiche refrigerated for up to 3 days.
• SERVING: To unmold the Quiche Lorraine, slide a sharp knife along the inside edge of the springform pan to loosen the quiche, then release the springform and remove the outer ring.
• Slice the Quiche Lorraine into portions, then serve cold or room temperature. You can also reheat portions in a 350°F (175°C) oven for 10 minutes. Serve the quiche with a lightly dressed green salad.
• STORAGE: Refrigerate leftover Quiche Lorraine in an airtight container for up to 3 days.