1. Preheat oven to 450 degrees.

2. In a medium bowl, whisk together cornmeal, baking soda, baking powder, sugar, and salt. Add in buttermilk and egg, and stir to combine.

3. Heat oil in a 10-inch cast-iron skillet over medium-high heat. Add cornmeal mixture, spreading evenly if necessary, and transfer skillet to oven. Bake until a cake tester inserted into the center comes out clean, about 15 minutes.

4. Meanwhile, preheat broiler. When cornbread is baked through, transfer to broiler; broil until top is golden brown. Serve.