In a large bowl (or in your mixer), add butter and sugars. Mix until creamed. Then add vanilla, and eggs. Mix until smooth.
Next add sourdough discard and peanut butter. Thoroughly mix.
Add salt and baking soda, along with one cup of flour. Continue to mix, adding one cup of flour at a time until fully combined.
Cover bowl and chill dough for at least one hour. (up to 24hours)
Preheat oven to 350degF.
Using a #40 (1 oz or 2 tbsp) scoop to portion out dough onto a parchment paper covered baking sheet. Using the back of a fork, make a crosshatch in the top of each dough scoop, pressing down slightly.
Place in oven to bake for 15 minutes.
Immediately remove cookies from the baking sheet to a cooling rack. Repeat with remaining dough.
Once fully cooled, transfer to airtight container for storage.