Beat butter at medium speed with an electric mixer until fluffy; gradually add sugar, beating well. Add eggs and egg yolk, one at a time, beating until blended after each addition. Beat in vanilla and next 3 ingredients.
In a large bowl, combine flour and next 3 ingredients; add to butter mixture alternately with whipping cream, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Pour batter into a well-greased and floured 12-cup Bundt pan.
Bake at 350° for 50 minutes or until a wooden skewer inserted in center comes out clean. Cool in pan on a wire rack 15 minutes; remove from pan. Poke holes in cake with a wooden skewer, and brush Rum Syrup over cake. Cool completely on a wire rack.
Note: For miniature Bundt cakes as pictured, fill each mini Bundt pan two-thirds full, and bake 35 minutes or until a wooden skewer inserted in center comes out clean.