Preheat your oven to 350°F (175°C).
Add green food colouring to marzipan and kneed until colour is even.
Beat Egg whites with mixer on high setting. Gradually add 1 cup of Brown sugar and keep mixing until stiff peaks form.
In a separate bowl, beat egg yolks and the remaining 1 cup of Brown sugar until thick and pale yellow.
Gradually add butter and baking powder to the egg yolk and sugar concoction.
Fold egg white and sugar concoction into egg yolk mixture.
Gradually, add the flour. (Sift in if you are using unsifted flour).
Divide batter into 3 equal parts (this depends on how you want to assemble the cake). Bake each part in the oven at the same time.
Bake for about 30 minutes or until soft top part springs back when gently pushed down from center.
Cool the 3 separate sponge cake part completely.