Preheat the oven to 375˚F (190˚C). Lightly grease cookie sheets
In a small bowl, mix together the milk and vinegar. Set aside to "sour".
In a medium bowl, mix together the flour, baking powder, baking soda and salt.
In a large bowl, mix together the shortening, peanut butter, white sugar, brown sugar and sour milk until fully combined. Slowly add the flour mixture, mixing together until fully combined.
Drop cookies 2 inches apart on the prepared cookie sheets.
Bake for 10-12 minutes, or until the edges are lightly browned. Let cool for 5 minutes, then transfer onto a wire rack to cool completely.
Cut the cookies in two and decorate with black icing and gummy fangs.