Line a small baking tray with parchment paper
Mix together the butter and sugar
Add the egg yolk and vanilla and mix
Add the flour, baking powder and salt and mix again
Mix through the chocolate chips
Split the dough into two - about 125g each
Place onto the tray and chill in the fridge for about an hour
Preheat the oven to 200ºc/180ºc fan
Bake for 12-14 minutes
