Preheat the oven to 375°F (190°C).
In a skillet, sauté the chopped onion until translucent.
In a large mixing bowl, whisk together the eggs and heavy cream until fully combined.
Add the cooked sausage, sautéed onion, shredded cheese, salt, and pepper to the egg mixture.
Pour the mixture into the prepared pie crust, spreading evenly.
Bake in the preheated oven for 35-40 minutes, or until the center is set and the top is golden.
Let the quiche cool for 10 minutes before slicing and serving.