Preheat oven to 350˚.

Beat together the peanut butter, shortening, butter, and both sugars in a large bowl with an electric mixer, 4 to 5 minutes, until fluffy and combined. Add the egg and vanilla extract and beat until combined.

Whisk together the flour, baking soda, and salt in a separate bowl. With the mixer on low speed, add the flour mixture to the peanut butter mixture and beat until well mixed.

Scoop the dough into 20 even portions (about 2 packed tablespoons each) and roll into balls. Flatten each ball slightly and arrange the cookies 2 inches apart on parchment paper-lined baking sheets. Press the center of each cookie with your thumb. Bake for 8 to 10 minutes, rotating the cookie sheets halfway through.

As you pull the cookies out of the oven, gently place 1 Reese's Mini just barely below the center of each cookie, allowing the warm cookie to melt the chocolate "body" into place. Then, very gently press 1 chocolate covered raisin or peanut "head" right above the Reese's Mini on each cookie. Allow the cookies to cool for 5 minutes on the baking sheets. Transfer the cookies to a wire rack to cool completely.

Once the cookies are cool, use the gel writing icing to draw 8 legs from the body of each spider. Allow the icing to set and enjoy!