Prepare the pastry crust: In a large bowl, whisk together the 250g (2 cups) of all-purpose flour and 5g (1 tsp) of salt. Add the 125g (½ cup + 1 tbsp) of cold, cubed unsalted butter. Using a pastry blender, your fingertips, or a food processor, cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining. This is crucial for a flaky crust.

Gradually add the ice water, 15-30ml (1-2 tbsp) at a time, mixing gently with a fork until the dough just comes together. Be careful not to overmix. You may not need all the water. The dough should not be sticky. Gather the dough into a ball, flatten it into a disc, wrap it tightly in plastic wrap, and refrigerate for at least 30 minutes (or up to 2 days) to allow the gluten to relax and the butter to firm up.

While the dough chills, cook the bacon: Place the 200g (7 oz) of diced thick-cut bacon in a cold skillet over medium heat. Cook, stirring occasionally, until the bacon is crispy and browned, about 8-10 minutes. Using a slotted spoon, transfer the bacon to a plate lined with paper towels to drain excess fat. Reserve about 15ml (1 tbsp) of the bacon fat in the skillet if desired for extra flavor in the filling, otherwise discard.

Roll out the dough: Lightly flour a clean work surface and your rolling pin. Unwrap the chilled dough and roll it out into a circle approximately 30-33cm (12-13 inches) in diameter and about 3mm (⅛ inch) thick. Carefully transfer the rolled-out dough to a 23cm (9-inch) tart pan with a removable bottom, or a standard pie dish. Gently press the dough into the bottom and up the sides of the pan. Trim any excess dough, leaving about a 1cm (½ inch) overhang. Crimp the edges decoratively.

Blind bake the crust: Preheat your oven to 190°C (375°F). Line the pastry shell with parchment paper or aluminum foil, ensuring it covers the bottom and sides. Fill with pie weights, dried beans, or uncooked rice. Bake for 15 minutes. Carefully remove the parchment paper and weights. Prick the bottom of the crust with a fork a few times. Return the crust to the oven and bake for another 5-8 minutes, or until lightly golden. This step prevents a soggy bottom.

Prepare the filling: In a medium bowl, whisk together the 3 large eggs, 300ml (1 ¼ cups) of heavy cream, and 150ml (⅔ cup) of whole milk until well combined. Stir in the 2g (½ tsp) of salt, 1g (¼ tsp) of freshly ground black pepper, and 1g (⅛ tsp) of freshly grated nutmeg. If using the reserved bacon fat, you can add it here for extra richness.

Assemble the quiche: Sprinkle the 100g (1 cup) of shredded Gruyère cheese evenly over the bottom of the partially baked pastry shell. Distribute the cooked, crispy bacon pieces over the cheese. Carefully pour the egg and cream mixture over the bacon and cheese, filling the pastry shell almost to the brim. Ensure the filling is evenly distributed.

Bake the quiche: Reduce the oven temperature to 180°C (350°F). Place the quiche on a baking sheet (to catch any potential spills) and bake for 30-40 minutes, or until the filling is set and the top is golden brown. The center should have a slight wobble when gently shaken; it will continue to set as it cools. If the crust edges start to brown too quickly, you can cover them with strips of aluminum foil.

Cool and serve: Remove the quiche from the oven and let it cool on a wire rack for at least 10-15 minutes before slicing and serving. This allows the filling to fully set. Quiche Lorraine can be served warm or at room temperature.