Step 1Place a 10-inch cast iron or heat-proof skillet in the oven. Heat the oven to 425 degrees.
Step 2Combine the cornmeal, flour, three-fourths teaspoon salt, baking powder and baking soda in a large bowl. In a small bowl, combine the melted butter, buttermilk, sour cream and egg. Fold the liquid ingredients into the dry ingredients to combine; don't overstir. Gently fold in the corn.
Step 3When the oven and skillet are hot, carefully remove the skillet. Grease it with bacon fat or oil. Pour in the corn bread batter and quickly put the skillet back in the oven.
Step 4Bake the corn bread 18 to 22 minutes, or until a toothpick inserted comes out clean. Remove the skillet from the oven to a rack to cool. After the bread has cooled, slice it, still in the skillet, into 8 to 10 wedges. Wrap each wedge in foil, then store the foil-wrapped wedges in a large sealable plastic bag for up to 1 day.
Step 5For the maple butter, place the remaining 12 tablespoons butter in a medium bowl. With a wire whisk or fork, whip the maple syrup into the butter until it is fully incorporated and light and fluffy. Season the butter with one-eighth teaspoon salt, or to taste. Cover and refrigerate until needed, but allow to come back to room temperature before serving.
Step 6To reheat the corn bread, heat a grill over medium-low heat. Place the foil-wrapped wedges on the grill, then cover and heat just a few minutes until warmed through, turning occasionally. Serve immediately with the softened maple butter.