Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a bowl mix melted butter, brown sugar, and granulated sugar until smooth.
Add sourdough starter, egg, and vanilla extract and mix until combined.
Stir in flour, baking soda, and salt until a soft cookie dough forms.
Fold in chocolate chips evenly throughout the dough.
Scoop cookie dough balls onto the prepared baking sheet leaving space between each.
Bake for 10–12 minutes until edges are golden and centers remain soft.
Let cookies cool on the tray for 5 minutes before transferring to a cooling rack.