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

Reduce oven temperature to 375°F (190°C).

In a large skillet over medium-high heat, cook the breakfast sausage until browned. Remove with a slotted spoon and set aside. Add the bacon to the skillet and cook until crisp. Remove, crumble, and set aside. Sauté the diced onion in the bacon fat until soft, about 5 minutes. Add the minced garlic and cook for 1 minute more.

In a large bowl, whisk the eggs. Slowly whisk in the heavy cream, whole milk, salt, pepper, and nutmeg until smooth. Stir in the shredded Gruyère and cheddar cheese.

Spread the cooked sausage, bacon, ham, and onion mixture evenly in the bottom of the pre-baked crust.

Carefully pour the egg mixture over the meat. Bake for 45-55 minutes, or until the center is just set (it should have a slight jiggle).

Let the quiche cool on a wire rack for at least 15 minutes before slicing and serving to allow the custard to fully set.