Preheat oven to 400 degrees F (200 degrees C). Whisk together the cornmeal, buttermilk, vegetable oil, and egg in a bowl to form a batter.
Melt the butter in a cast-iron skillet over medium heat, and swirl the melted butter all over the bottom and up the sides of the skillet. Let the butter heat until it gives off a faint toasted fragrance; pour the batter into the hot skillet.
Place the skillet into the preheated oven, and bake until golden brown, 25 to 30 minutes.