Preheat the oven to 425°. Warm a 9-inch cast-iron skillet over moderate heat. Add the oil 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 skillet; the oil should bubble. Transfer the skillet to the oven and bake for about 18 minutes, or until the center springs back when gently pressed. Turn the corn bread out onto a rack to cool. If using for stuffing, coarsely crumble the corn bread.
The unmolded corn bread can stand at room temperature for 2 days.