In a large skillet, melt butter over medium heat. Add sliced onions and cook until golden brown, stirring occasionally. Add brown sugar, balsamic vinegar, salt, and pepper. Cook for an additional 5 minutes, stirring occasionally.
Roll out pie crust and place in a 9-inch pie dish. Spread onions over the crust and top with Parmesan and mozzarella cheese.
Bake for 25 minutes or until pie crust is golden brown.
Let cool for 10 minutes before serving.
Interesting Facts
Vidalia onions are only grown in the state of Georgia.
Vidalia onions are known for their sweet flavor.
Vidalia onions are a major cash crop for the state of Georgia.