Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large bowl, cream together butter, brown sugar, and granulated sugar until fluffy.
Mix in sourdough starter, egg, and vanilla extract until smooth.
Whisk together flour, baking soda, and salt in a separate bowl.
Gradually fold dry ingredients into the wet mixture until just combined.
Stir in chocolate chips evenly.
Scoop tablespoon-sized dough balls onto the prepared baking sheet.
Bake for 10–12 minutes until edges are lightly golden and centers are soft.
Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack.