Make sure pie crust is completely defrosted. Bring frozen crust to the refrigerator the night before, or hours prior.
Pre-heat oven to 425 degrees F. Place bacon on a baking sheet lined with aluminum foil and bake bacon for 12-20 minutes. Check at 12 minute mark, and bake for longer if needed. When done, drain grease. Cut bacon into 1 inch pieces.
While waiting for bacon to be done in the oven, slice onions. Heat up skillet. Add butter and once butter is melted, saute onions until it is soft and slightly brown. Add a pinch of salt to onions and stir. Remove and set aside.
Pre-heat oven to 375 degrees F.
In a large bowl, whisk together eggs, heavy cream, salt and pepper.
Place pie crust into a pie pan (9" x 2"). Add bacon, spinach, white cheddar and caramelized onions. Pour egg mixture into pie pan.
Bake for 30-35 minutes or until done. Check for doneness by inserting a toothpick into the filling, and if it comes out clean the pie should be done.