Sift flour, cornflour and baking powder. Grease and line a small rectangular pan.
Combine margarine, vanilla, sugar, eggs, milk and dry ingredients in a medium bowl.
Beat with mixer until combined, then on medium speed for 3 minutes until smooth.
Scrape into prepared pan and bake for the specified time or until a skewer inserted comes out clean.
Let cake stand for 5 minutes before turning out onto a wire rack to cool. Dust with icing sugar, if desired.
To Serve: Cake can be served with fruit or ice cream.