In a mixing bowl combine flour, sugar, baking powder, baking soda and salt.
With a pastry blender, cut in butter until mixture resembles coarse crumbs. If you don’t have a pastry blender, grate the frozen butter with a box grater and incorporate with your fingers.
Make a well in center of dry mixture; set aside.
In another bowl combine starter and egg.
Add the wet mixture all at once to dry mixture. Using a fork, stir just until moistened.
Turn out onto lightly floured surface. If the dough is too sticky add flour until it becomes easier to handle.
Add chocolate chips and mint. Fold in carefully.
Drop heaping spoonfuls onto an ungreased baking sheet.