In a mixing bowl, dissolve yeast in warm water. Add milk, sugar, shortening, egg, salt and 2 cups flour; beat until smooth. stir in enough remaining flour to form a soft dough.

Turn onto a floured surface; knead until smooth and elastic, about 4-6 minutes. Place in a greased bowl, turn once to grease top. Cover and let rise in a warm place until doubled, about 30 minutes.

In a skillet, cook beef and onion until meat is no longer pink; drain. Stir in tomato sauce. Remove from the heat; set aside.

Punch dough down; divide into 16 pieces. On a lightly floured surface, gently roll out and stretch each piece into a 5-in. circle. Top each circle with two pieces of cheese and about 3 Tablespoons beef mixture. Bring dough over filling to center; inch edges to seal.

Place seam side down on a greased baking sheet. Cover and let rise in a warm place until doubled, about 20 minutes. Bake at 400ºF for 8-12 minutes or until golden brown. Serve warm. Refrigerate leftovers.