In a large skillet, cook bacon until crisp; drain bacon and discard pan drippings. In the same skillet, cook onions in butter until tender. Cool.
In a large bowl, combine sour cream, flour and salt; add eggs. Stir in the bacon and onions; set aside.
Separate crescent roll dough into four rectangles. Pat dough onto the bottom and 1 in. up the sides of a greased 9-in. square baking pan, stretching as needed. Pinch edges together to seal. Pour onion mixture over dough.
Bake at 375° for 30 minutes or until the topping is set and crust is golden. Cool slightly before cutting into small squares. Serve warm.