Grease and lightly flour a 9- to 10-inch springform pan, at least 2 3/4 inches
deep. In a large bowl, beat egg yolks until thick and light-colored; gradually beat
in sugar, beating until thick and pale. Sift flour with baking powder and salt.
In small bowl, combine hot water, lemon juice, and orange peel. Add flour mixture
to beaten egg yolks alternately with hot water mixture, stirring to blend after
Using clean beaters, beat egg whites with cream of tartar until soft peaks form.
Stir a fourth of the beaten egg whites into flour mixture, then fold in remaining
egg whites carefully but thoroughly. Pour batter into prepared pan.
Bake at 350 degrees F for 40 to 45 minutes or until cake is golden brown and
begins to pull away from the sides of the pan and springs back when touched lightly
in the center. Let cool completely in pan on wire rack.
To make syrup, combine sugar, water, orange peel, and lemon peel in a small pan
over high heat. Bring to a boil then cook rapidly for 3 minutes. Remove from heat
and let cool. Blend in the 1/3 cup rum.
To make custard, place eggs and sugar in the top of a double boiler and mix thoroughly.
Scald half and half; gradually stir into egg mixture. Place double boiler over gently
simmering water. Cook, stirring constantly, until custard coats a meta spoon in
a velvety smooth layer (10 to 15 minutes). Remove from heat and mix in vanilla extract.
Place top of double boiler into ice water to stop cooking; stir custard frequently
until cool. Stir in rum. Whip 1 cup of cream until soft peaks form when beaters
are lifted. Fold into cooled custard.
To assemble dessert, remove pan side from cake, leaving cake on base. Carefully
cut cake horizontally into 3 equal layers and lift off the top two layers. Replace
the pan sides around pan bottom holding the remaining cake layer.
Drizzle cake bottom layer with a third of the syrup, then cover with a third
of the custard. Carefully place the middle layer of cake in the custard, sprinkle
this layer with another third of the syrup, then another third of the custard. Set
top cake layer in place. Sprinkle with remaining syrup, pour on remaining custard,
and spread evenly. Cover cake lightly to protect top. Refrigerate for at least 6
hours or until the next day.
Remove pan sides.
Whip the 1/2 cup whipping cream until stiff. Sweeten slightly
with sugar and spread on cake top and sides. Cut into wedges.