- Step 1: Preheat the oven - Preheat your oven to 375°F (190°C). Line baking sheets with parchment paper or leave them ungreased. 
- Step 2: Mix the wet ingredients: In a large mixing bowl, beat together ½ cup shortening and 1 cup creamy peanut butter until smooth. Add ½ cup packed light brown sugar and ⅓ cup granulated sugar (reserving ⅓ cup sugar for rolling the cookies), and beat until light and fluffy. Then mix in 1 large egg, 2 tablespoons milk, and 1 teaspoon vanilla extract until well combined. 
- Step 3: Combine the dry ingredients - In a separate medium bowl, whisk together 1 cup all-purpose flour, ⅓ cup unsweetened cocoa powder, 1 teaspoon baking soda, and ½ teaspoon salt. 
- Step 4: Make the dough - Gradually add the dry ingredients to the peanut butter mixture, mixing just until everything is combined and a soft dough forms. 
- Step 5: Shape and roll the cookies - Roll dough into 1-inch balls (about 1 tablespoon each). Roll each ball in the reserved ⅓ cup granulated sugar and place them 2 inches apart on the prepared baking sheet. 
- Step 6: Bake - Bake for 8–10 minutes, or until cookies are lightly browned and set around the edges. 
- Step 7: Add the spider bodies - Immediately press 1 Rolo or miniature peanut butter cup (upside down) into the center of each warm cookie. Transfer cookies to a wire rack to cool slightly. 
- Step 8: Attach the eyes - While the chocolate candy is still soft, gently press 2 candy eyes onto each one. 
- Step 9: Chill to set - Refrigerate the cookies for 10–15 minutes to allow the chocolate to firm up. 
- Step 10: Add the spider legs - Use black decorating icing to pipe 8 spider legs (4 on each side) around the candy center. 
- Refrigerate again for about 10 minutes to set the icing before serving.