In a mixer, cream the brown sugar and butter together. Add the eggs and vanilla and mix. Next add the salt, baking soda, sourdough starter, and slowly add the flour. Mix on medium speed for a minute or two. Add the chocolate chips and mix just till combined.
Bake right away or let it ferment in the fridge for a couple hours or overnight.
Drop by spoonful on cookie sheet and bake in a preheated 350 degree oven for 10-12 minutes until lightly browned on top.
Place on parchment paper and let cool. Store in an airtight container.