Preheat the oven to 375=B0. Dice 3 T butter and refrigerate. In a large saute pan, cook the onions in the remaining butter and oil, starting over medium heat and gradually reducing to low heat, for about 1 hour, until the onions are very tender, golden, and reduced considerably in size. Stir continuously for the last 15 min and be very careful not to let them burn. They will be extraordinarily sweet and delectable. Discard any burned parts. Sprinkle the onions w/the flour, using a strainer or sifter, and saute another 2 or 3 minutes. Beat the eggs and cream in a bowl with a third of the cheese. Stir in the onions, then pour the mixture into the quiche shell. Sprinkle with remaining cheese and dot with the diced butter. Bake 25-30 minutes or until browned and set.