1. Preheat oven to 375°F (190°C). Line baking sheets with parchment paper. In a large bowl, cream together butter and granulated sugar until light and fluffy. Beat in egg and vanilla extract. In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt. Gradually add dry ingredients to wet ingredients, mixing until just combined. Roll dough into 1-inch balls and place them 2 inches apart on prepared baking sheets. Bake for 8-10 minutes, or until edges are set. Let cool on baking sheets for a few minutes before transferring to a wire rack to cool completely. While cookies cool, prepare the peanut butter filling: In a medium bowl, combine peanut butter, powdered sugar, and milk. Mix until smooth and spreadable. Add more milk if needed for desired consistency. Once cookies are cool, pipe or spread about 1 tablespoon of peanut butter filling onto the flat side of each cookie. Unwrap Hershey’s Kisses and gently press one kiss into the center of the peanut butter filling on each cookie, creating the witch hat shape. Serve immediately or store in an airtight container at room temperature.