Preheat oven to 375°F. In a large skillet, cook ground beef and onion over medium heat for 8 to 10 minutes or until beef is thoroughly cooked, stirring frequently. Season with salt and pepper. Drain.

Stir in marinara sauce; cook until thoroughly heated.

In a medium bowl, combine mozzarella cheese and sour cream; mix well.

Pour hot beef mixture into an ungreased 9 ½ or 10-inch glass deep-dish pie pan or 11x7-inch (2-quart) glass baking dish. Spoon cheese mixture over beef mixture.

Unroll crescent dough, press seams together and lay over cheese mixture. In a small bowl, mix Parmesan cheese and butter. Spread evenly over dough.

Bake at 375°F for 18 to 25 minutes or until deep golden brown.