Preheat oven to 350 degrees F. Prepare two large baking sheets by spraying with cooking spray or lining with parchment.
In a large bowl or the bowl of a stand mixer, cream together the butter, peanut butter, white sugar, and brown sugar until well blended.
Add the egg and vanilla and mix until smooth.
Add the flour, baking soda, and salt, and mix until blended.
Add milk as needed if the dough is crumbly. The dough should be thick but should hold together well.
Fold in the chocolate chips until well distributed.
Scoop tablespoon sized scoops of dough onto the prepared baking sheets and mash down with a fork.
Bake 10-12 minutes, or until lightly golden around the bottoms.
Serve warm with cold milk!