Step 1: Preheat your oven to 375°F (190°C). Roll out the pie dough and fit it into a 9-inch pie plate. Trim and crimp the edges.
Step 2: Line the crust with parchment paper and fill with pie weights. Bake for 15 minutes. Remove weights and paper, then bake for another 5 minutes until the bottom is set. Lower oven temperature to 350°F (175°C).
Step 3: In a medium bowl, whisk together the eggs, heavy cream, salt, pepper, and nutmeg until well combined and slightly frothy.
Step 4: Distribute the shredded Gruyère cheese, crumbled bacon, sautéed spinach, and shallots evenly across the bottom of the pre-baked crust.
Step 5: Slowly pour the egg and cream mixture over the fillings, ensuring everything is evenly distributed.
Step 6: Place the quiche on a baking sheet and bake for 35-45 minutes, or until the edges are set and the center jiggles just slightly.
Step 7: Remove from the oven and let the quiche cool for at least 15-20 minutes before slicing to allow the custard to set properly.