Combine the peanut butter and sugars in a stand mixer with a paddle attachement. Beat until fully mixed. Depending on the type of peanut butter you use, the mixture will either be light and fluffy or in tiny crumbles. Either is fine!
Add the egg, then vanilla, mixing to combine each.
In a separate bowl, combine the flour, baking soda, and baking powder. Mix well, then add to the peanut butter mixture. Mix to combine.
If the mixture is extremely dry (and does not hold together at all when you try to form a ball, add milk 1 Tbsp at a time until it does. The dough should NOT be sticky or wet at all, and will barely hold together in a ball.
Mix in the chocolate, then form into small balls. Do not flatten. Bake for 8-10 minutes.
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/soft-peanut-butter-chocolate-chunk-cookies/