Add the vanilla extract and beat quickly again. Add the flour and continue to work until the mixture pulls together as a sticky dough. 

Roll the dough into a rough, thick sausage shape, cover with cling-film and pop in the fridge for an hour or so.

Remove from the fridge and cut into two parts (it’s easier to roll when a little smaller) and work the dough into thick rolls (the thicker the roll, the bigger the cookie will be). Pre-heat the oven to 175ºC (350ºF) and line a large baking tray with greaseproof paper.

Cut each roll into six slices with a thickness of around 1.5cm, ending up with 12 cookies. These are large but if you wanted to make them smaller just work the dough roll until it is longer and thinner. Place the cookies on the tray and gently push around four blueberries into the tops (if they are smaller cookies you will use fewer blueberries).

Bake for around 18-20 minutes until the edges are golden brown. Remove from the oven, sprinkle with a little sugar and leave to cool completely. Enjoy!