Preheat the oven to 450 with the iron skillet in the oven. After the oven is preheated, leave the skillet in for an additional 5 minutes.
Whisk together dry ingredients: cornmeal, sugar, salt, baking powder and baking soda in a large bowl.
Add the large egg and buttermilk and whisk until smooth.
Remove the hot skillet from the oven and add the butter. Allow it to melt and brown. Swirl around the melted butter so that the edges and bottom are coated.
Pour in the cornbread batter and bake for 12-15 minutes, or until cooked thoroughly.