If adding chopped peanuts, finely chop nuts by hand or in a food processor. Set aside.
Mix butter and peanut butter together until well combined, then add sugar, brown sugar, and egg. Beat until light and fluffy.
Add dry ingredients, mixing well. If using, stir in chopped peanuts and chocolate chips.
Form dough into 1.5" balls, place them about 2" apart on an ungreased cookie sheet, then flatten slightly with a fork. Bake for 9-10 minutes, until the cookies are a little golden. Transfer them to a rack to cool completely.
Keep cookies in an airtight container or, even better, freeze them in zip-topped bags. These cookies are great right out of the freezer or thawed.
Notes
*To make these vegan, use a vegan butter and substitute a flax or chia "egg": 1 Tablespoon of ground flax meal or chia seeds mixed with 3 T warm water. Let it sit for 5 minutes to gel.**To make these gluten free, simply substitute the all purpose and whole wheat flours for a one-to-one GF baking flour.