Heat the oven to 400°F. Spray the bottom and sides of an 8-inch square pan or 9-inch round cake pan with the cooking spray.
In a 1-quart saucepan, heat the butter over low heat until melted.
In a large bowl, beat the melted butter, milk and egg with a fork or wire whisk until well mixed. Add the cornmeal, flour, sugar, baking powder and salt all at once; stir just until the flour is moistened (batter will be lumpy). Pour batter into the pan; use a rubber spatula to scrape batter from bowl. Spread batter evenly in pan and smooth top of batter.
Bake 20 to 25 minutes or until golden brown and a toothpick inserted in the center comes out clean. Serve warm.