Step 1: Roll out the pie crust to a 12-inch circle and carefully transfer it to a 9-inch pie dish or quiche pan. Press firmly into the bottom and sides, then trim excess dough, leaving a 1/2-inch overhang. Fold under and crimp decoratively. Chill for at least 30 minutes.
Step 2: Preheat your oven to 400°F (200°C). Line the chilled pie crust with parchment paper and fill with pie weights, dried beans, or rice.
Step 3: Blind bake the crust for 15 minutes. Remove the parchment and weights, then prick the bottom all over with a fork. Continue baking for another 5-7 minutes, or until lightly golden. Remove from oven and reduce oven temperature to 375°F (190°C).
Step 4: While the crust is baking, cook the bacon pieces in a skillet over medium heat until crisp. Using a slotted spoon, transfer the cooked bacon to a plate lined with paper towels to drain.
Step 5: In a large bowl, whisk together the eggs, heavy cream, whole milk, Dijon mustard, salt, black pepper, and nutmeg until well combined and slightly frothy.
Step 6: Sprinkle half of the cooked bacon and half of the grated Gruyère cheese evenly over the bottom of the partially baked pie crust.
Step 7: Carefully pour the egg and cream mixture over the bacon and cheese in the crust.
Step 8: Top with the remaining bacon and Gruyère cheese.
Step 9: Carefully transfer the quiche to the preheated oven (375°F/190°C).
Step 10: Bake for 35-45 minutes, or until the center is just set (it should have a slight wobble when gently shaken) and the top is golden brown. If the crust or top browns too quickly, loosely tent with aluminum foil.
Step 11: Remove the quiche from the oven and let it cool on a wire rack for at least 15-20 minutes before slicing and serving. This allows the custard to fully set.