Preheat the oven to 180ºC/gas mark 4. Line a 12-hole muffin tray with fairy cake cases. Put the butter, sugar and lemon zest into a large bowl and beat together until pale and fluffy.
Add a little beaten egg to the butter mixture and beat. Continue to add the egg a little at a time, beating in as you go, along with 2 tbsp flour. Sieve the remaining flour and baking powder on top.
Gently fold the mixture together using a large spoon until all the flour is mixed through. Spoon the mixture evenly into the paper cases, then put the tray in the oven and bake for 12-15 minutes, until a skewer inserted into the centre comes out clean and the cupcakes are risen and golden. Leave to cool.
Sieve the icing sugar in a bowl and add 1 tbsp lemon juice, then mix until smooth. Add 1-2 drops of food colouring and decorate the cakes with the icing and sugar flowers.