Allow butter, eggs, and egg yolk to stand at room temperature for 30 minutes. Meanwhile, generously grease and lightly flour a 10-inch fluted tube pan; set aside. In a small bowl stir together flour and baking powder. In a medium bowl combine milk and rum. Using the tip of a small sharp knife, scrape out seeds from vanilla beans. Stir vanilla seeds into milk mixture; set aside.
Preheat oven to 325 degrees F. In a large mixing bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Gradually add granulated sugar and brown sugar, beating about 10 minutes or until light and fluffy. Add eggs and egg yolk; beat for 1 minute. Alternately add flour mixture and milk mixture to butter mixture, beating on low speed after each addition just until combined. Pour batter into the prepared pan, spreading evenly.
Bake about 45 minutes or until a wooden toothpick inserted near the center comes out clean. Cool cake in pan on a wire rack for 10 minutes. Remove cake from pan; cool completely on wire rack. Serve with whipped cream, rum caramel, and red fruit (raspberries or pomegranates both work great!)
You can use vanilla extract instead of vanilla bean but the vanilla bean will have a more powerful flavor. If using extract use 1 teaspoon. Or you may just use one vanilla bean and a little extract to save some money :)