sentence: heat the butter in a pan sentence: cook the finely chopped onions in it sentence: mix flour salt egg and water sentence: make the mixture to a dough sentence: put the cooked onions with grated potatoes and mix salt pepper and cheese in it sentence: take small flat portions of the dough and place some mixture on top sentence: wrap them up to pierogi shape sentence: boil them in boiled water and fry them with onion and butter and then serve