Preheat oven to 425°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, cornmeal, baking powder, baking soda, and salt in a large bowl. Add buttermilk and egg; stir just until combined.
Place an 8-inch cast-iron skillet in the oven for 5 minutes, and remove from oven. Add 2 1/2 tablespoons butter to pan; swirl to melt and lightly grease pan. Stir melted butter into batter. Add batter to preheated pan. Bake at 425° for 20 minutes or until lightly browned and a toothpick inserted in center comes out clean. Cool 5 minutes in pan. Slice into 8 wedges.
Combine remaining 2 1/2 tablespoons butter, molasses, bourbon, and rind in a small bowl; beat with a mixer at medium speed until combined (about 1 minute). Serve butter with warm corn bread.