Cut the potatoes and carrots into slightly larger cubes, put them in a saucepan with water (the vegetables must be covered with water) and cook them with the teaspoon of vegetable stock.
Chop the onion, fry the tartare in oil and add the onion.
Mash the cooked potatoes and carrots in a bowl, add about 3-4 tablespoons of the stock and stir in the tartare.