Preheat oven to 400°F (200°C). Press the pie crust into a 9-inch deep-dish pie plate. Line with parchment paper, fill with pie weights, and bake for 15 minutes. Remove weights and parchment, then bake for another 5-7 minutes until lightly golden. Set aside.

In a large skillet, cook chopped bacon until crisp. Remove and drain on paper towels. In the same skillet, cook the ground sausage until browned, drain excess grease. Crumble the bacon and set aside with the sausage and diced ham.

In a large bowl, whisk together eggs and heavy cream. Stir in the cheddar cheese, Gruyère cheese, chopped onion, salt, pepper, and nutmeg.

Spread the cooked bacon, sausage, and ham evenly over the bottom of the pre-baked crust. Pour the egg mixture over the meat.

Bake at 375°F (190°C) for 35-45 minutes, or until the center is just set (it should jiggle slightly).

Let the quiche cool on a wire rack for at least 10-15 minutes before slicing and serving. This allows the custard to set.