Shift the flour, corn flour and baking powder in a sieve. Set aside the sieved powder mixture.
Mix the sugar and butter in a bowl and beat well to make a cream.
Add milk powder and vanilla essence. Continue beating.
Add egg, one at a time and whisk continuously.
Add the flour mixture, a little at a time, preferably in 3-4 parts on to the egg batter mixture. Make sure the flour mixture is not dumped in to the center of the batter, but rather slowly added on to the sides of the bowl. Fold the powder in to the batter and mix well.
Take 1/3 of the batter on to a separate bowl. Mix in the coco powder.
Grease a baking tray and pour the batter without the chocolate to make one layer.
Add in a layer with all of the chocolate mixture. Pour the top layer with the rest of the plain batter.
With a fork slowly spiral and zigzag through the layers to make a “marble” pattern. Do not stir too much.
Place the tray in a micro-oven and bake for 8-10 minutes at Medium-High powder.