Beat peanut butter and shortening until well mixed, then beat in the two sugars until light. Add the egg, milk, and vanilla and beat until fluffy. Whisk the flour, baking soda, and salt together, then add in 3 batches to the peanut butter mixture, beating well between additions.
Roll dough into 1/2 inch balls. Roll in granulated sugar and place on ungreased baking sheets. Bake 5-7 minutes and remove from oven. Immediately press a chocolate chip into the center of each cookie. Let cookies cool a minute, then transfer to a wire rack to cool completely.
The cookies will keep for several days at room temperature in an airtight container.