Combine sugar and margarine in a bowl and beat together using a mixer or a whisk until light and fluffy. Add eggs one by one as you mix and vanilla essence.

Combine flour and baking powder in a bowl. Pour the flour mixture into the sugar - margarine mixture and mix together and pour into cupcake tins.

Bake at 180°C for 35 minutes. As the cake cools prepare your buttercream. Beat the margarine until light and add icing sugar gradually. Pipe the cream onto the cupcakes