Preheat oven to 375. In a large skillet, cook ground beef and onion over medium heat until beef is thoroughly cooked. Drain, stir in pasta sauce, cook until heated through.

In medium bowl combine mozarella cheese and sour cream, mix well. Pour hot beef mixture into deep dish pie pan, spoon cheese mixture over beef mixture. Unroll crescent dough over cheese mixture. In a small bowl, mix parmesan cheese and butter, spread evenly over dough, bake at 375 for 18-25 minutes.