Preheat oven to 375 degrees Fahrenheit.

In a mixing bowl or stand mixer, add butter, shortening, vanilla extract, and sugars. Beat until light and fluffy, approx. 5-10 minutes.

Scrape down the sides of the bowl and add egg, egg yolk, peanut butter, and sourdough discard. Mix until just combined.

In a separate bowl, mix flour, baking soda, and salt.

Slowly add dry ingredients to wet ingredients. Mix until fully combined.

Using a cookie scoop, place balls of dough in a small bowl of granulated sugar and roll until fully covered.

Place sugar-covered dough balls onto a prepared baking sheet 2 inches apart. Use a fork to gently flatten the cookies.

Bake at 375 for 8-10 minutes or until the top looks just set.

Allow to cool on the baking sheet for at least 5 minutes before moving to a cooling rack.