1Preheat oven to 375 degrees F ( 190 degrees C )
In a a large bowl, cream together the peanut butter, butter, white sugar, and brown sugar until well blended. Beat in the egg, milk, and vanilla one at a time. Combine the flour, baking powder, and salt; stir into creamed mixture. Roll about a tablespoon of dough into balls. Place cookies 2 inches apart onto ungreased cookie sheet. Press each ball in a criss cross pattern with a floured fork.
Bake for 8 to 10 minutes in the preheated oven or until edges are very lightly browned.