How to Make It
Add peanut oil to a 10-inch cast-iron skillet; place skillet in oven, and preheat to 450°F. (Do not remove skillet while oven preheats.)
While oven preheats, whisk together cornmeal, flour, sugar, 21/2 teaspoons salt, baking powder, and baking soda in a medium bowl. Stir in buttermilk until smooth; stir in eggs, then stir in butter.
Carefully remove skillet from oven; pour hot oil from skillet into cornbread batter, stirring until blended. Working quickly, sprinkle remaining 1/4 teaspoon salt in bottom of skillet, then immediately pour batter into hot skillet (do not stir), and return to oven.
Bake at 450°F until top is golden brown, about 22 minutes. Immediately invert cornbread onto a wire rack; let cool completely, about 1 hour and 30 minutes.