Line a quiche pan or springform pan (28 cm diameter) with the puff pastry, pulling the edge up a little. Preheat the oven to 200 ° C top / bottom heat (180 ° C convection).
Peel the onion and cut into 1/4 rings. Fry in olive oil until light yellow.
Drain the sauerkraut and pineapple cubes well. Mix the sour cream with the eggs in a bowl. Stir in the sauerkraut, onions and pineapple pieces, season with salt and pepper. Spread half of the mixture on the puff pastry. Spread all of the cheese on top. Cover with the remaining sauerkraut mixture.
Bake the sauerkraut cake for about 35 - 40 minutes until it has turned golden brown. Let cool down for 10 minutes before cutting.