Place 1 tablespoon oil in an (11-inch) cast-iron pan and swirl it around. Place pan in the oven; preheat oven to 375º.
Combine remaining 1/2 cup oil, milk, eggs, and sour cream, beating well with an electric mixer. Combine flour and remaining ingredients in a large bowl, stirring well with a whisk. Add oil mixture to flour mixture, beating until combined. Carefully remove hot skillet from oven. Spoon batter into pan.
Bake at 375º for 30 minutes or until cornbread is lightly browned and it springs back when pressed lightly. Cool in pan on a wire rack.