Beat the butter until it is light and fluffy.
Then add in the icing sugar (powdered sugar) and mix until everything is well combined.
Beat in the vanilla extract and the egg yolk until you have a pale creamy batter.
Fold in the lemon zest and juice.
Then fold in the flour to bring everything together. Then chill it in the fridge for at least 30 minutes.
Once the chilling time is up preheat your oven to 190C / 375F / Gas mark 5 and take your dough out of the fridge. Line 2 baking sheets with parchment paper.
Roll the dough out till it is 5 millimetres thick, and cut out 2 inch (5 centimetre) rounds and place them on your baking trays with a little space between them.
Pop them in your oven but keep a close eye on them, as they will brown quickly once baked.
While your cookies are cooling it’s time to make your icing.
In a small bowl place your icing sugar, half of your lemon juice and yellow food colouring if using and mix all together. Add more lemon juice a little at a time to get the right drizzling consistency.
Then drizzle over your cooled cookies.
Kept in an airtight tin these cookies will stay fresh for up to 5 days.