Preheat your oven to 375 degrees Fahrenheit and let it fully preheat. Place the unbaked 9-inch pie crust in a pie dish.

Heat a large skillet over medium-high heat and add the bulk sausage, breaking it into small crumbles as it cooks. Cook for 6 to 8 minutes, stirring occasionally, until the sausage is fully cooked and no longer pink. Drain excess fat using a slotted spoon.

Spread the cooked sausage evenly over the bottom of the unbaked pie crust. Sprinkle the shredded cheddar and Swiss cheese on top, distributing them evenly.

In a medium mixing bowl, crack all 6 eggs and whisk them together until the yolks and whites are fully combined. Add the heavy cream, milk, salt, pepper, garlic powder, and nutmeg, whisking until completely smooth and well blended.

Carefully pour the egg and cream mixture over the sausage and cheese in the crust, pouring slowly to ensure even distribution. Stop pouring when the filling reaches about 1/4 inch from the rim of the pie dish.

Allow the assembled quiche to sit at room temperature for 5 to 10 minutes before baking.

Place the quiche in your preheated oven and bake for 40 to 45 minutes, until the top is golden brown and the center is set but still slightly jiggly in the very middle. A knife inserted about 1 inch from the edge should come out clean.

Remove the quiche from the oven using oven mitts and let it rest on the counter for 10 to 15 minutes before slicing. This allows the custard to set fully.