Shift all-purpose flour and cocoa powder.
Beat margarine and mix sugar and beat till smooth and fluffy. Mix 1 tbsp. milk and 2 tbsp. all-purpose flour mixture and beat with spatula. Repeat the process till all the flour is used. Mix vanilla extract and beat the mixture. Fill this mixture in the piping bag with star nozzle. Grease and dust oven tray and make 2 inches long star fingers in the tray. Leave space between the two. Bake in oven for 20 minutes at 350 degree F. When cool apply icing between the two fingers.