Preheat oven to 350 degrees F (175 degrees C.) Heat butter in a large skillet. Saute the sliced onions until soft and translucent; set aside.
Line a 10 inch quiche pan with bread. Place cooked onions in an even layer over the bread. In a small bowl, combine eggs, sour cream, salt, white pepper and caraway seeds. Pour egg mixture over bread and onions, then lay bacon strips over top.
Bake in the preheated oven 25 to 30 for minutes, or until filling is set.