Set your oven to 425°F (220°C) with the rack in the middle position.

Place your 10-inch cast iron skillet in the oven as it preheats. Let it get blazing hot, at least 15 minutes.

In a large bowl, whisk together the cornmeal, flour, baking powder, baking soda, and salt until evenly distributed.

In a separate bowl, whisk together the eggs, buttermilk, and vinegar (if using) until smooth.

Pour the wet ingredients into the dry ingredients. Stir with a spatula or wooden spoon until just combined. You want no dry streaks of flour, but lumps are fine. Stop stirring the second it comes together. Overmixing activates the gluten in the flour and turns your cornbread tough and cakey.

Carefully remove the screaming hot skillet from the oven. Drop the butter in and swirl as it melts. It should foam and start to brown slightly. Tilt the skillet to coat the bottom and about an inch up the sides.

Pour about 2 tablespoons of the melted butter from the skillet back into your batter and give it one or two quick stirs. This adds richness throughout the bread, not just on the edges.

Pour the batter into the hot, buttered skillet. It should sizzle immediately. That sizzle is the sound of a perfect crust forming. Smooth the top gently with the back of a spoon.

Return the skillet to the oven and bake for 20-25 minutes until the top is golden brown, the edges have pulled slightly away from the sides of the pan, and a toothpick inserted in the center comes out clean or with just a few moist crumbs.

Let it rest in the skillet for 10 minutes before cutting into wedges. If you want the crust on top, flip the whole thing out of the skillet onto a cutting board (carefully, with oven mitts), then flip it back crust-side up.

Grease an 8x8 or 9x9 baking dish with butter or cooking spray. Pour batter in and bake at 425°F (220°C) for 22-28 minutes. You won't get the same crust, but the interior will still be great.