Place a well-seasoned 12-inch cast iron skillet on the center rack of the oven and preheat oven to 375°F.

Meanwhile, in a large bowl, whisk cornmeal with salt, baking powder, baking soda, and sugar (if using).

In a separate bowl, whisk buttermilk with eggs until homogenous. Whisking constantly, drizzle in all but 1 tablespoon melted butter.

Whisk liquid ingredients into dry ingredients just until thoroughly mixed; avoid over-mixing.

Pour remaining 1 tablespoon melted butter into preheated skillet and carefully swirl to coat bottom and sides. Scrape batter into prepared skillet, smoothing the top gently with a rubber spatula. Bake until cornbread is lightly browned on top and a skewer inserted into center comes out clean, about 45 minutes.

Let cool for about 15 minutes in skillet, then serve warm. (Cornbread does not keep well and will lose its texture as it cools, so its best to eat it while its still fresh.)