Heat oven to 200C/180C fan/gas 6. Line 2 baking trays with baking parchment. Melt the butter, sugar and syrup in a small saucepan. Mix in the vanilla, remove from the heat and leave to cool for 10 mins.
Sieve the flour and bicarbonate of soda into a bowl. Pour in the melted butter mixture and the egg, and stir together to form a stiff-ish dough. Pop the dough in the fridge for 10 mins to chill and firm up.
Roll the dough out on a floured surface to 5mm thick, then stamp out 15 circles using a 7.5cm round cookie cutter; you may need to re-roll the trimmings to get 15 cookies. Make a hole at the top of each circle with the end of a pencil.
Place on the baking trays and bake for 12 mins until golden, swapping the trays around halfway through. Cool on a wire rack. Decorate the cookies (see below), making sure the hole is at the top of each one. Will keep for 3 days in an airtight container.