In a large bowl, dissolve yeast in water. Add sugar, egg, salt and 1 cup of flour; beat on low speed for about 3 minutes. Add enough remaining flour to form a soft dough. Turn onto a floured surface and knead until smooth and elastic, about 6-8 minutes. Place in a greased bowl and turn once to coat the top. Cover and let rise in a warm place until doubled, about 1 hour.

Meanwhile in a large skillet, cook ground beef over medium heat until no longer pink; drain. Add cabbage, onion, salt and pepper. Cook over medium heat for about 15 minutes, or until vegetables are tender. Stir in cheese. Remove from heat and set aside to cool.

Punch down dough and divide into 12 pieces. Roll each piece into a 5-6 inch circle. Top each circle with about 1/4 cup of the filling. Fold dough over to meet in the center and pinch edges to seal.

Place seam-side down on a greased baking sheet. Cover and let rise in a warm place until doubled, about 30 minutes. Brush with butter. Bake at 350 degrees F for 20 minutes or until golden brown. Serve warm.