Preheat the oven to 375°F and line a large baking sheet with parchment paper or a silicone baking mat and set aside.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
In a large bowl with a hand mixer or stand mixer fitted with a whisk attachment, cream together the shortening, peanut butter, brown sugar, milk, and vanilla on medium speed.
Add in the egg and beat just until combined.
Add in the flour mixture all at once and mix just until combined.
Use a medium cookie scoop to portion out the dough. Roll each scoop into a ball and roll it in granulated sugar before placing on the baking sheet at least 2 inches apart.
Bake the cookies for 9 to 10 minutes, the edges should be firm but the centers will be slightly puffy and soft. Remove from the oven and use the back of a round teaspoon to indent the center of each cookie. Transfer to a wire rack and allow the cookies to cool for 20 minutes.
Melt the chocolate wafers on 30-second intervals in the microwave and then transfer to a piping bag fitted with a #2 round tip. Make the spider legs on the cookies by starting from the outside and going back to the center 8 times to create 8 legs. I recommend doing this on wax or parchment paper for easy cleanup.
Then place a truffle in the center of each cookie and use the melted chocolate to carefully stick the candy eyes to the truffles.