Wash the potatoes and cook them in a little water.
In the meantime, wash, peel and slice the carrots. Loosen the chard leaves, wash them, separate the leaves from the ribs and cut the ribs into strips. Sauté them with the carrots in butter, pour in the milk and simmer for about 20 minutes until soft.
Finely chop the chard leaves and cook in the butter for about 15 minutes. Peel the potatoes. Puree the potatoes with the vegetables, 1 egg yolk, the oil and 1 tablespoon.