Preheat your oven to 350F/175C.

Add the brown and white sugar to a bowl with the butter and mash them together with a fork.If you'd prefer, you can cream the butter and sugar using a hand mixer or stand mixer.

Add the peanut butter and mix until well combined (if the peanut butter is a little hard, soften it in the microwave).

Add the egg, vanilla and sourdough starer to the bowl and mix together until well combined.

Now, add the all purpose flour and baking powder to the bowl and bring it together to a stiff dough.

You can chill the dough in the fridge for up to 2 days at this point.

When you're ready to bake the sourdough discard peanut butter cookies, take the dough out of the fridge and allow to sit at room temperature for around 10 minutes.

Roll the dough into small balls (I've done 20g balls). Use a fork to press the cookies down with a criss cross pattern.

Bake the sourdough peanut butter cookies for 10 to 12 minutes at 350F/175C.

Allow the cookies to cool completely on the baking tray before transferring them to a glass jar.