Put flour in bowl. Press hollow in middle and add salt and egg yolks and 1/2 cup water. Using knife or big spoon, mix egg yolks first with water and then some of flour. Slowly add rest of water until mixture forms dough. Knead dough with both hands until workable and free of lumps. If dough is too sticky, add some flour. Dough should form solid ball. Sprinkle thin layer of flour onto flat surface. Divide dough into 3 pieces. Roll out 1 piece of dough until thin. Keep remaining dough covered under damp towel. Cut dough in circles about 2" in diameter. Repeat with remaining dough. Combine beef, pork, onions, garlic and mushrooms in bowl. Place 1 ts meat mixture on each dough circle, then bend other side and press to seal, forming half-moons. Use some water, if necessary, brushed lightly on edges to make them stick. Keep finished pelmeni either on wax paper or board sprinkled with flour. Pelmeni can be frozen at this point and cooked later. Cook 20 to 25 pelmeni at a time, uncovered, in plenty of rapidly boiling lightly salted water, about 5 minutes. Repeat until all pelmeni are cooked. Serve pelmeni either in clear soup (beef or, preferably, poultry) or as main course with pepper vinegar, sour cream, brown butter or spicy tomato sauce. Makes 60 pelmeni. 540 cal; 25% fat.