Cream butter, turbinado sugar, and brown sugar until light and fluffy
Add egg, vanilla, and active sourdough starter. Mix until smooth
Add dry ingredients and mix until just combined. Dough should be thick
Fold in chopped chocolate (keep 20g of each chocolate out for topping)
Scoop into 75g dough pucks and flatten slightly
Freeze 30 minutes then move to fridge for 2 hours
Bake at 350°F (177°C) for 12-15 minutes, until edges are set and centers look soft
Immediately press extra chocolate chips or chunks on top (optional but recommended)
Cool 5 minutes on the tray, then move to a rack to finish setting
