First peel the potatoes, cut them into pieces and cook them in salted water, then drain them. Let the milk warm up. Mash the potatoes and add the warm milk and a good piece of butter, stir with a whisk and season with salt.
Bring the sauerkraut to the boil with a little water and simmer for a while.
Cut the peppers and onions into fine cubes and fry a little in oil in a pan. Add the sauerkraut and mix everything well, season with salt. Then just fold in the mashed potatoes.