In a large mixing bowl beat butter and peanut butter with an
electric mixer on medium to high speed for 30 seconds. Add the
granulated sugar, brown sugar, baking soda, and baking powder.
Beat until combined, scraping sides of bowl occasionally. Beat in
the egg and vanilla until combined. Beat in as much of the flour as
you can with the mixer. Stir in any remaining flour. Add milk (from
1/2 Tablespoon to 1 Tablespoon just enough to make the dough
moist and creamy. Add chocolate chips and mix till just
incorporated. If necessary, cover and chill dough about 1 hour or
until easy to handle.