Start by making the crumble. In a bowl, combine the ingredients then put it into the fridge whilst you make the cookie.
Cream together the butter and sugar.
Add in the yoghurt and extract - mix until combined.
Add in the dry ingredients - mix until just combined (do not overmix!).
Fold in the blueberries and white chocolate chips.
Line a 15cm baking tin and gently press the cookie dough into the pan.
Cover with your crumble then put this into the fridge for at least 30 minutes to chill.
Preheat oven to 170 degrees C fan and bake for 20-30 minutes, or until golden.
Cool in the pan and then enjoy!
