In a stand mixer fitted with the paddle attachment (or mix with a spoon and bowl), combine the butter and sugar. Beat on medium speed, gradually increasing to high until the butter is light and fluffy, and pale in color; about 3 minutes.

Add the sourdough starter, egg, egg yolk, and vanilla, and beat until combined.

Slowly beat in the flour, salt, and baking powder. Do not over mix.

Place the dough covered in a small Tupperware or wrapped in plastic wrap. Be sure the dough is tightly sealed so it doesn’t become dry on the outside.

Ferment the covered dough at room temperature for 8+ hours. I typically will make the dough in the morning so it’s ready by evening or overnight! You can refrigerate but before baking just bring it to room temperature for a few hours :)

When you’re ready to bake, preheat your oven to 350°F (177°C).

Divide and roll the cookie dough into 10-12 cookies, depending on how large you want your cookies to be. I like each cookie to weigh around 20-30g.

Press the middles down slightly and add your lucky charms on top by pressing down.

Bake for 6-8 minutes or until lightly browned on the sides.

Remove from the oven and let cookies fully cool on the baking sheet. Enjoy!

Store sourdough cookies in an airtight container at room temperature for 3 days or in the refrigerator for 6 days. To reheat, bake in a 350°F (177°C) oven for 5 minutes.