Peel the potatoes and cook them whole in salted water until tender, but do not boil them. Cool down.
Cut the pork tenderloin into small plates 3 cm thick, i.e. make the so-called medallions. Chop the meat, season with salt and pepper.
Cut a large onion into large pieces.
Finely chop the parsley.
In sunflower oil (or olive oil, as you like), fry the meat on both sides until a crust forms. Reduce the heat and fry it until tender.
Remove the finished meat from the pan and set aside for now.
In a frying pan, pour the onion and fry until soft. Add the butter and fry the onion until golden brown.
Cut the potatoes into slices 1 cm thick or slightly larger and add them to the onion. Gently stir with a spatula and fry a little, just 1 minute.
Add the meat broth. You can use a cube. I prepare the broth and pour it into large silicone muffin molds (120 ml) and store it in the freezer, then add it to the dishes as needed. You can pour the broth into cellophane bags and also freeze.
As soon as the frozen broth melts in the pan (and not frozen properly warmed up), add the parsley, stir.
Spread the meat medallions on the potatoes, a sprig of rosemary (or a couple of pinches of dry), cover the pan with a lid and heat everything over a low heat so that the cooled meat becomes hot, and the rosemary lets out all its flavors. A delicious and flavorful dish is ready.