Saute onions in butter until soft. Remove and cool. Add eggs and sour cream. Season with salt and pepper. Pour into unbaked pie crust. Sprinkle with Parmesan cheese.
Bake at 450F for 20 minutes. Reduce to 325F and bake for 20 more minutes. If it starts to get too brown, lay a piece of foil on top.
Let sit 5-10 minutes before slicing.
Recipe by Opsreys Journeys at https://www.ospreysjourneys.com/?p=2771