Heat milk to lukewarm, pour into a bowl; add yeast. Mix with you fingers. Add a cup of the flour, and mix to form a ball. Cover the bowl, and set in a warm place. Let the sponge rise until double in bulk. Punch down. Add vegetable oil, egg yolks, salt and remaining flour, mix well, then knead to make a stiff dough. (Add more water or flour, if necessary.) Cover and let rise again. Meantime, brown the meat in butter. Add onion, and cook until light brown. Mix in tomato sauce and parsley, and cook abt. 15 to 20 min. Stir in grated cheese. Lightly flour a bread board and turn dough out onto it; knead until elastic. Divide into small pcs. Flatten these with your hands, or roll into thick round shapes. In the center of each, place a tbs. of the meat mixture. Fold over dough to form a half-moon shape. Brush edges with a little egg white, and pinch to seal. Flatten the piroski slightly and place on a buttered baking sheed. Set aside in warm place to rise again, but for less time. Deep-fat fry until a deep golden color. Remove with slotted spoon, drain, and serve hot. Makes about 15 to 18 piroski. NOTE 1: These can be baked instead of fried. To bake follow the directions above to the final rising, then brush tops with egg white, and bake in preheated 350 F. oven until golden brown. NOTE 2: The filling can be of chicken, ham, fish, or hard-cooked eggs. For any of these, chop the filling and mix with Bechamel sauce, or mashed potaotes. NOTE 3: You can also make sweet piroski by adding 3 tbs. sugar when you add the salt. Fill dough with marmalade and chopped glazed fruit. Bake as in Note 1 above, and top with confectioners sugar.