Preheat the oven to 425°. Warm two 9-inch cast-iron skillets over moderate heat. Add 1 1/2 tablespoons of the oil to each and heat.
Meanwhile, in a bowl, sift the flour with the sugar, baking powder and salt. Stir in the cornmeal. Add the milk and eggs and stir lightly. Add the melted butter and stir just until blended. Scrape the batter into the hot skillets; the oil should bubble. Transfer the skillets to the oven and bake the corn breads for about 18 minutes, or until the centers spring back when gently pressed. Turn the corn breads out onto a rack to cool.
Make Ahead: The unmolded corn breads can be stored at room temperature for up to 2 days.