Mix the rye flour with a pinch of salt, sugar and water until you get a smooth and firm dough, let it rest for an hour. Meanwhile, cook the peeled potatoes in boiling water until soft. Mash them and add a knob of butter. Season with salt and pepper and mix all the ingredients.
In a saucepan, bring the milk to a boil and pour the rice. Cook for about 20 minutes so that the rice absorbs the milk creating a creamy dough. Add the rice to the potatoes and stir. Roll out the rye dough keeping a thickness of ½ cm and cut out the oval shapes. Pour the filling and close by curling the edges inwards. Brush the surface with whipped egg yolk and melted butter. Bake in a hot oven at 200 ºC for about 20 minutes. Let sit and serve lukewarm.