Bring a large pot of salted water to a boil. Add potatoes and cook until tender but still firm, about 15 minutes; drain.
Combine flour, eggs and salt. Mix in a little water at a time until dough is somewhat stiff. Roll dough in small sections about 1/4 inch thick. Using a large biscuit cutter or drinking glass, make circle cuts.
To make filling: Mix together potatoes, cheese, salt, pepper and onion salt. Fill each with 1 to 2 tablespoons of the potato mixture, fold over and seal edges. To cook, bring a large pot of water to boil, carefully dropping in one at a time; stir once. They are done when they float to the top.