Whisk together the cream, milk, eggs, salt and pepper in a medium bowl. Add the onions and 1 cup of the cheese and stir to combine. Pour the mixture evenly into the pie crust. Sprinkle the remaining cheese on top of the pie.
Bake in the preheated oven until a knife inserted in the center comes out clean, about 40 to 45 minutes. If the crust starts to get too brown, cover it with foil. Remove the pie from the oven to cool on a wire rack.
Let the pie cool for at least 10 minutes before cutting.