Crack the eggs into a mixing bowl, and whisk them together until evenly combined. Add the milk, cream, onion powder, salt, and pepper to the bowl, whisking again to evenly combine. Set aside.
5 large eggs, 1/2 cup whole milk, 1/2 cup heavy whipping cream, 1 tsp onion powder, salt & pepper
Spread the cheese out evenly in the bottom of the pie crust, then top with the thinly sliced onions.
1 9 inch frozen deep dish pie crust, 1 cup shredded white cheddar cheese, 1 1/2 -2 cups thinly sliced onions
Pour the egg mixture into the crust, then use a fork to gently agitate the onions so that all of the egg mixture seeps down. The mixture will fill the pie crust to the brim.
Place the filled pie crust on a baking sheet, and bake at 400° for 55-60 minutes, or until the egg is set and the pie crust is golden brown.
Let the quiche rest for 5-10 minutes, then slice and serve warm.