Preheat your oven to 350°F (175°C).

In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy (about 2-3 minutes).

Add the egg, sourdough starter, and vanilla extract, mixing until well combined.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt.

Gradually add the dry ingredients to the wet mixture, stirring just until combined. Fold in the chocolate chips or any mix-ins.

Use a cookie scoop or a tablespoon to drop rounded balls of dough onto ungreased baking sheets, leaving space between each cookie.

Place the baking sheets in the preheated oven and bake for 10-12 minutes, or until the edges are golden brown.

Let the cookies cool on the baking sheet for 5 minutes before transferring them to a cooling rack.