2. In a small saucepan, bring 1/2 cup water to a boil over high heat. In a large bowl, combine 1/2 cup of the cornmeal and the boiling water. Stir to blend—the mixture should become a thick mush.
3. In a medium bowl, whisk the remaining 1-1/4 cups cornmeal with the flour, sugar, baking powder, salt, and baking soda to blend.
4. Add the buttermilk, sour cream, and eggs to the cornmeal mush and whisk to blend.
5. When the oven and pan are fully heated (after about 20 minutes), add the dry ingredients to the wet ingredients and mix with a wooden spoon until just blended. Do not overmix.
6. Remove the hot pan from the oven and add the butter pieces, tilting the pan to swirl the butter around until it’s melted and the pan is well coated. (The butter may brown; that’s fine.) Immediately pour the melted butter over the mixed batter and stir to combine—a half-dozen strokes with a wooden spoon should be plenty. Scrape into the hot pan.
7. Bake until the cornbread pulls away from the sides of the pan and is golden on top, 18 to 20 minutes. Immediately turn the bread out onto a rack. Cool for 5 minutes. Serve hot.