Rum Syrup: In a small pan, mix sugar, orange peel, orange juice, lemon peel,
lemon juice and cinnamon. Bring to a boil over medium-high heat. Boil, stirring,
just until sugar is dissolved. Remove from heat and let cool, then stir in rum and
vanilla extract. Set aside.
Cake: Beat eggs and sugar until thick and lemon-colored. Add flour, baking powder,
orange peel and butter. Beat until well blended. Spread batter in a greased, floured
9-inch springform pan with a removable rim.
Bake at 375 degrees F until cake just begins to pull away from sides of pan and center springs back when lightly pressed (about 20 minutes).
Set warm cake in pan on a rack; set rack over a plate to catch any drips. Pierce
cake all over with a fork. Slowly pour Rum Syrup over cake; let cool. Just before
serving, remove pan rim; garnish cake with orange segments, if desired, and mint