Preheat your oven to 350°F (175°C).
In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Add the active sourdough starter, egg, and vanilla extract. Mix until combined.
In a separate bowl, whisk together the rolled oats, baking soda, salt, and any optional chocolate chips or nuts.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Scoop tablespoons of dough onto a prepared baking sheet lined with parchment paper, leaving space between each cookie.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden.
Remove from the oven and let them cool on the baking sheet for 5 minutes before transferring to a wire rack.
