For Sponge: Preheat the oven to 180 degree Celsius. Grease and line an 8 inch square tin.

Put the butter and sugar into a bowl and beat until creamy and lighter in color.

Add egg one at a time and beat thoroughly.

Sieve the cocoa and flour into a bowl and add a third of the flour mixture at a time into the sugar, egg and butter and mix well. You should have a smooth thick batter.

Bake for 25 minutes till the sponge springs back.

For Assembly: Line a deep vessel with plastic wrap.

Trim crusts of the prepared sponge.

Use a large serrated knife to cut 1 inch wide strips of the sponge.

Line the base and side of the vessel with the cake strips, slightly overlapping, and press to seal.

Brush cake with rum and allow it to cool.

Spoon softened ice cream into the cake lined vessel. Smooth the surface.

Top with the reserved cake layer, trimming cake to fit, if necessary.

Press gently to enclose.

Cover with plastic wrap.

Place in fridge for 7-8 hours to chill, or until firm.