Draw a pencil shape onto a thin piece of cardboard. 3cm wide by 9cm long works well, with one end slightly rounded and the other end triangular. Cut out the shape.
Cream butter and sugar together. Beat in egg and vanilla essence. Sift in flour, cornflour, cinnamon, ginger and nutmeg and mix until combined. Knead gently with your hands to bring the dough together if required. If the dough is too soft, chill until firm enough to roll out easily.
Preheat oven to 180ºC bake and line two large oven trays with baking paper.
Turn dough out onto a lightly floured surface and use a floured rolling pin to roll out to 5mm thick. Place the pencil cut out on top and carefully use a sharp knife to cut around the edges. Use a spatula to lift onto the prepared trays. Repeat until the dough is used up, re-rolling as required.
Bake pencil cookies for 10-15 minutes (depending on how soft or crispy you like them), until lightly golden. Leave to cool on trays for 5 minutes, then transfer to a cooling rack to cool completely before icing.
Using the whisk attachment of an electric beater or stand mixer, whisk together icing sugar, glucose syrup, milk and vanilla essence, slowing adding water as required until icing is a smooth, pipeable consistency.
Divide icing between smaller bowls and add food colouring as desired, leaving one bowl of icing white. Transfer icing to squeezy bottles or piping bags and decorate cookies to look like pencils.
Leave until icing has hardened before transferring to airtight containers.
Icing can take a couple of hours to harden completely. If you want to add finer details, you will need to wait for the first lot of icing to dry (you can speed this up by placing the cookies in the fridge for 10 minutes).
Cookies keep well in an airtight container for 5 days.