Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until well combined and fluffy.
Stir in the sourdough starter, vanilla extract, and egg until all ingredients are fully incorporated.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture and stir until just combined.
Fold in the chocolate chips until evenly distributed throughout the cookie dough.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, leaving space between each cookie.
Bake in the preheated oven for 10-12 minutes or until the edges are lightly golden and the centers are set but still soft.
Once baked, remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a cooling rack.