Beat butter and granulated sugar at medium speed with an electric mixer until light and fluffy. Add eggs, egg yolk, and vanilla, beating until blended. Add lemon rind, beating until blended. Gradually add rum and banana liqueur, beating until blended. (Batter will look curdled.)
Stir together flour and next 3 ingredients; add to batter alternately with whipping cream, beginning and ending with flour mixture. Beat batter at low speed just until blended after each addition. Pour batter into a greased and floured 10-inch Bundt pan.
Bake at 350° for 55 to 60 minutes or until a long wooden pick inserted in center of cake comes out clean.
Cool in pan on a wire rack 15 minutes. Pierce cake multiple times using a metal or wooden skewer. Pour Rum Syrup evenly over cake. Let stand 45 minutes. Remove from pan; cool completely on a wire rack. Sprinkle evenly with powdered sugar before serving.