Prepare the Crust. Roll out the pie crust into a 9-inch pie pan, trimming any excess. Pre-bake the crust at 375°F for about 10 minutes.
Cook the Bacon. Fry the bacon in a skillet over medium heat until crispy. Remove and let it drain on paper towels. Crumble into bite-sized pieces.
Sauté the Onion. In the same skillet, sauté the onion in the bacon drippings until soft and translucent.
Mix the Custard. Whisk together the eggs, heavy cream, milk, salt, and pepper in a large bowl until smooth.
Assemble the Quiche. Layer the crumbled bacon, sautéed onion, and shredded cheddar cheese evenly in the pre-baked crust. Pour the custard mixture over the top.
Bake to Perfection. Bake the quiche at 375°F for 35–40 minutes, or until the filling is set and the top is golden.
Cool and Serve. Let the quiche cool for 10 minutes before slicing. Serve warm or at room temperature.