Preheat oven to 400. Place a 10-inch cast iron skillet in oven for 30 minutes.
In large bowl combine flour, cornmeal, salt, baking powder and sugar. Make a well in the center and add milk, eggs and melted butter. Stir just until moistened.
Remove skillet from oven and add bacon fat to skillet. Swirl around to coat bottom and sides, then pour in cornbread mixture. Smooth the top with a spatula, then place in oven and bake about 25 minutes, or until brown.
If you like, you can spread 2 tablespoons of butter on top of hot cornbread to melt.