Sourdough peanut butter cookies feature sourdough discard in a classic buttery cookie. The perfect salty-sweet combination! With a hint of tang from discard, they're complex and delicious.
Preheat the oven to 350°F (180°C) and line two baking sheets with parchment paper.
Add the peanut butter, butter, starter, brown sugar, white sugar, egg, and vanilla to a large mixing bowl.
Use an electric hand mixer to blend until fluffy and light, about 2-3 minutes.
Add the flour, baking powder, baking soda, and salt to the bowl. Mix until just combined.
Roll the dough into 14 approximately equal balls and place them onto the prepared baking sheets. Leave about 3cm (1 inch) space between.
Press the cookies with the tines of a fork to create a crosshatch pattern in the tops.
Bake for 12-14 minutes, or until lightly golden and the edges feel just firm to the touch.
Cool the cookies for 5 minutes on the trays before carefully removing to cool fully on racks. Keep in an airtight container for up to a week at room temperature or freeze for up to a month.