Because Tatars eat кыдыбы.
http://besthomerecipes.ru/images/x_4832559361.jpg
http://www.spbtatarlar.ru/images/fotos/fotos/63967994.jpg
We only make them with mashed potatoes. I haven't eaten any other kind.
And yes, the main thing is not to add any onions, otherwise you'll end up with boiled onions in the mashed potatoes. What could be worse? So, potatoes cooked in milk, in this kind of dough, and coated with butter (you need to melt it in a pan).