Position a rack in the center of the oven and preheat to 350 F. Lightly spray a 9-inch cake pan with cooking spray.
Spread the butter and brown sugar evenly on the bottom of the prepared pan. Bake until the mixture is melted and bubbly, about 4 - 5 minutes. Remove the pan from the oven and cool for a few minutes. Peel the bananas and cut them on a diagonal into thin slices. Place banana slices on the bottom and along the sides of the pan.
Cake: Whisk together the flour, Clabber Girl Baking Powder, nutmeg, and salt into a medium-size bowl. In a separate bowl, whisk together the brown sugar, oil, eggs, milk, rum, and vanilla. Make a well in the center of the dry ingredients, add the egg mixture, and stir just until blended. Do not overbeat. Pour into the pan and spread evenly to the edges, covering any exposed banana slices.
Bake until the center springs back when pressed gently with your finger, about 18 - 22 minutes. Immediately invert and unmold onto a plate. Cool briefly and serve.
* You can omit the rum and substitute an additional 3 tablespoons milk to keep the wet to dry ratio intact.
Yield: 10 servings