Boil the potatoes in salted water for approx. 20 minutes, drain, allow to evaporate a little, press through the potato press. Mix this mixture well with the butter, an egg yolk and nutmeg while being slightly warm.
Put everything in a piping bag and press rosettes with the large, star-shaped opening onto a baking sheet lined with baking paper. Mix the second egg yolk with a little water and brush each potato rosette with it. Bake in the 175 ° oven for about 10 minutes until the potatoes are golden yellow.