Preheat your oven to 375°F (190°C). Place your 9-inch pie crust in a pie dish, ensuring it sits snugly against the edges.

In a skillet, heat over medium heat and add the chopped bacon. Cook until crispy and golden, about 6-8 minutes. Remove and drain on paper towels.

In the same skillet, add chopped onion to the reserved bacon fat. Sauté over medium heat for about 3-4 minutes, until soft and translucent.

In a large mixing bowl, crack in the eggs and add heavy cream, salt, pepper, and nutmeg. Whisk until smooth and well-combined, about 1-2 minutes.

Layer the cooked bacon, sautéed onions, and shredded Gruyère cheese at the bottom of the prepared pie crust. Pour the whisked egg mixture over the top.

Place the assembled quiche in the preheated oven and bake for about 40 minutes, or until the center is set and the top is golden.

Let the quiche cool for about 10 minutes before slicing. Serve warm or at room temperature.