Cream together the butter and sugar until pale and light.
Add the lemon zest, egg, vanilla or lemon extract and salt and mix well.
Gradually add the 450g of flour and mix until combined and smooth.
Using your hands, bring the dough together into a ball. Flatten into a disc, wrap in clingfilm and chill for 2 hours or until firm
Lightly dust the work surface with the remaining flour. Roll the dough out to a thickness of around 3-4 mm, use the Cookie Cutters to stamp out the biscuits. Re-roll the dough off-cuts and stamp more shapes.
Place on the Baking Tray and Bake for about 12 minutes on the middle shelf of the preheated oven until lightly golden and firm to the touch. Leave the cookies to cool on the baking tray for about 10 minutes, then transfer to a wire rack until cold.
Decide how many colours you’d like to use, and divide the icing into the appropriate amount of bowls. Tint each with food colouring pastes.
Spoon 1-2 tbsp icing into an icing bag with a small nozzle and pipe an outline around the edge of each cookie. Leave to dry for 10 minutes.
Add a drop more water to the remaining icing so that it is slightly runnier than the outline icing. Using a teaspoon, carefully and evenly ice inside the outline. Leave to dry before piping on any detail.