1. Heat the oven to 180°C, 160°C fan, Gas 4. Line a cup cake tin with 12 paper cupcake cases.
2. Place the butter and sugar in a mixing bowl and beat with a wooden spoon or electric mixer until light and fluffy. Gradually beat in the eggs a little at a time until smooth, adding a little flour if the mixture curdles.
3. Stir in the flour, baking powder, lemon zest and vanilla extract until smooth.
4. Place heaped dessertspoon full in each cupcake case and bake for 20-25 minutes until golden brown and just firm to the touch.
5. Leave in the tins for 5 minutes, then place on a wire rack to cool.
Mix fondant icing sugar with water as directed on the pack, then stir in a drop of food colouring to give the desired colour. Spoon a little icing over each cake. Insert a small candle in the centre of each cake.