Line a round quiche pan with the puff pastry. Preheat oven to 200 degrees (convection 180 degrees)
Peel the onions and cut into half rings. Melt the margarine in a pan, fry the onions in it until light brown.
Mix the eggs, sour cream, caraway seeds and cheese in a bowl, season with salt and pepper. Quickly stir in the onions and pour the mixture into the mold. Bake in the preheated oven for 35 minutes. Let cool down for 10 minutes before cutting.