Cream together, the butter, granulated sugar and dark brown sugar.
Blend in egg.
On LOW speed, blend in the starter discard and vanilla.
Whisk together the dry ingredients. Mix in until thoroughly incorporated.
Stir in the chocolate chips.
Allow dough to rest for about 15-30 minutes.
Preheat oven to 375°F.
Using a medium cookie scoop, place dough at least 2 inches apart onto parchment-lined baking sheet.
Bake 10-12 minutes or until lightly brown around edges and top. You should be able to see them rise around the 4 minute time mark.
Allow to set on pan for 3-5 minutes before removing cookie to cooling rack.