Preheat oven to 350F. Whisk egg whites until stiff. In a separate bowl, cream
egg yolks and sugar. Add lemon juice and peel, flour and whipped egg whites.
Bake in a greased and floured springform pan for 40-45 minutes or until
inserted toothpick in the middle of the cake comes out clean. When cake is
completely cool, cut it in half horizontally (it's best to use dental floss to
do so). Spread a thin layer of filling on the bottom half. Top with sliced
bananas, and then spread another thin layer of filling over them. Cover with
the other half and glaze with the remaining filling.

For the filling:
Cream egg yolks and sugar. Add vanilla extract, flour and milk and. Place in
double boiler and stir until creamy. When the filling has cooled, mix with
softened butter, until creamy.