FOR THE DOUGH: Dissolve the yeast and a pinch of sugar in the warm water. Sprinkle in a teaspoon of flour and leave for 15 minutes in a warm place. Pour into a bowl, mix in the softened butter, sifted flour and salt, the milk and the beaten eggs, and knead into a smooth dough. Leave to rise until it has doubled in volume. Knead again and roll out. Cut out in small circles: you will be folding these in half to enclose the filling in a semi-circle or canoe shape. Brush the inner edges with a little milk to help them seal firmly. Then either brush the piroshki with egg and bake in a moderate to hot oven for about 10 minutes, until golden brown: or fry them, uncoated, in deep fat. FOR THE MEAT FILLING: Lightly fry the onion in the oil or butter, add the meat and cook for 5 minutes. Combine in a bowl with the seasoning and herbs and allow to cool. Pirozhki often come out rather dry because of the small quantities of filling which cannot, as with a pie, be moistened by the last-minute addition of stock. Both suet and frozen stock in little chips have been recommended to me by conscientious Russian pastry cooks to cure this fault. My objections are that suet makes the pirozhki undesireably fatty, while the chipped stock needs forethought and a sledgehammer, both of which go missing when I am in a hurry. A better solution, I think, is to use stock either naturally or artificially jellied with gelatine. Add 2 teaspoons, finely chopped, to the mixture when it is absolutely cold from the refrigerator, bind with egg and use immediately. FOR THE MUSHROOM FILLING: Chop the fresh mushrooms into quarters and cook gently in butter with finely chopped herbs for 15 minutes. Season, add a little chopped onion, chopped hardboiled egg or rice or both, and enough sour cream to make a fairly moist filling. FOR THE BUCKWHEAT FILLING: Cook the kasha in salted water for about 15 minutes until soft but not mushy. Drain well and combine with chopped hard-boiled egg, chopped fried onions, and chopped mushrooms saute'ed in butter. Add seasoning and herbs to taste. Allow the mixture to cool thoroughly in the refrigerator and add little pieces of very cold butter. Use immediately. ...These are basic traditional fillings, but there is plenty of scope for invention along non-Russian lines; for example, egg and mushroom filling, moistened with butter....