Cream butter + turbinado + brown sugar.
Add egg, vanilla, and active starter.
Add dry ingredients and mix until thick (add 5–10g more flour if sticky).
Scoop into 75g pucks and flatten slightly.
Roll pucks in cinnamon sugar.
Freeze 30 minutes → move to fridge for 2 hours.
Bake at 350°F for 12–15 min until edges are set and centers look soft.
Cool 5 minutes on the tray, then move to a rack. (They finish setting as they cool!)
