Preheat oven to 350 degrees F. Prepare two cookie sheets by lining them with parchment paper.
In the bowl of a stand mixer with paddle attachment, (you can also use a hand help mixer) cream together the peanut butter, butter, white sugar, and brown sugar until well blended.
With mixer on low, add in the egg, milk, and vanilla one at a time.
Combine the flour, baking powder, baking soda, and salt; stir into creamed mixture.
Using a 1/4 cup measuring cup, section out 1/4 cup of dough, roll into a ball, then flatten on cookie sheet.
Each cookie sheet should fit 4 cookies. Press a fork into the flattened cookie to achieve the traditional peanut butter cookie appearance.
Bake for 8 to 10 minutes or until edges are lightly browned.
Recipe makes 12 giant peanut butter cookies.
Allow cookies to cool before adding ganache.