2 x 12 cup muffin tins,
24 muffin cases
Preheat the oven to 180ºC, fan 160ºC, gas mark 4. Put the sugar and butter in an electric mixer and beat until pale and fluffy.
Beat the eggs lightly in a small bowl and add slowly to the mix, using medium speed. If the mixture starts to curdle, add a little of the flour. When the eggs and butter mixture is well combined, mix in the liqueur (if using) and the remaining flour at slow speed.
Divide the mixture between the muffin cases using two teaspoons or a piping bag with a wide nozzle [no.10].
Bake for 18-20 minutes or until the sponge is lightly golden and springs back to the touch.
Leave to cool before icing.
To make shamrock decorations:
Roll out the green sugarpaste to about 3mm thickness using a little icing sugar to prevent sticking. Cut out shamrock shapes and put to one side.
Prepare the royal icing as on the pack and cover the cupcakes with a spoon or pallet knife
[Add green colouring if desired].
Place the green shamrock shapes on the icing before completely set.
Wait until fully set before serving.