Deep-fry or fry the frikandel in the deep fryer or in the pan.
Cut the puff pastry into pieces of the same size so that you can roll the frikandel in it afterwards.
In the meantime, preheat the oven to 200 ° C top / bottom heat.
After deep-frying or roasting, degrease the frikandel with a kitchen towel and place on the puff pastry. Place some of the chopped onions next to the frikandel and then top with some ketchup and mayonnaise. Roll up and place in the oven until the rolls have a nice color.
The rolls are filling up in themselves, but if you like, you can also serve french fries and / or a green salad.