Heat the butter and rapeseed oil in the pan and fry the onions, cut into rings, until golden brown. Dust the chopped liver with a little flour and then add to the onions in the pan. Fry, turning several times, and only season with salt and pepper at the end of the cooking time.
In the meantime, peel the potatoes, cut them into cubes and cook them in enough water with the vegetable stock as required. Then mash to a pulp and season with butter, nutmeg and salt.
Arrange and serve on plates.
This goes well with fresh salad of your choice.
Tip: If you glaze the onion a little with sugar, the liver has a slightly sweet taste (but it is a matter of taste).