1-Preheat and prepare crust: Preheat your oven to 375°F (190°C). Roll out the pie crust to fit a 9 to 12-inch tart or deep-dish pie pan. Trim excess dough, then freeze the shell for at least 30 minutes to prevent shrinking during baking.

2-Blind bake the crust: Line the crust with parchment paper or foil and fill with pie weights or dried beans. Bake for 35–40 minutes until lightly golden. Remove weights and brush the inside with egg white to seal and keep the crust crisp.

3-Cook the bacon: While the crust bakes, cook the diced bacon over medium heat until crisp and fat is rendered, about 10 minutes. Drain bacon on paper towels and reserve about one tablespoon bacon fat in the pan.

4-Caramelize onions: Add diced onions or shallots to the reserved bacon fat. Cook over medium-low heat for 3–5 minutes until softened and caramelized but not browned.

5-Prepare custard mixture: In a medium bowl, whisk together eggs, half-and-half (or milk and cream), salt, black pepper, nutmeg, and cayenne pepper if using, until smooth and frothy.

6-Assemble quiche: Spread caramelized onions evenly into the pre-baked crust. Layer half the bacon, then all grated cheese over the onions, and top with remaining bacon.

7-Pour custard and bake: Carefully pour custard mixture over fillings without disturbing layers. Bake at 325°F (160°C) for 45–50 minutes or at 350°F (175°C) for 30–40 minutes, until custard is set but still slightly wobbly in the center and lightly golden on top. A knife inserted should come out clean.

8-Rest and garnish: Cool the quiche for 10–15 minutes before slicing. Garnish with chopped parsley or chives if desired, then serve warm, at room temperature, or cold.