In a large mixing bowl, use an electric mixer to cream together the peanut butter, butter, and brown sugar.
Mix in the sourdough discard until well blended.
Add the eggs, one at a time, and mix until smooth. Stir in the vanilla.
In a separate, medium mixing bowl, whisk together the dry ingredients: flour, baking powder, baking soda, and salt. Don't add the chocolate chips just yet.
Slowly mix the dry ingredients into the wet ingredients, and then fold in the chocolate chips.
Use a cookie spoon to drop dough onto a lightly greased baking sheet, be sure to even space the cookies about 2 to 3 inches apart to give room for expansion.
Use a fork to gently press a criss-cross pattern into the cookies.
Preheat the oven to 350 degrees Fahrenheit (176 degrees Celsius), and bake for 8 to 12 minutes. The cookies will be lightly browned on the edges and still soft looking in the middle.
Allow the cookies to rest on the baking sheet for 5 minutes to finish baking as they cool.