Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large bowl, cream together the butter and sugar until light and fluffy.

Beat in the egg, milk, and vanilla extract until well combined.

In a separate bowl, whisk together the cocoa powder, baking soda, salt, and flour. Gradually add the dry ingredients to the wet ingredients and mix until combined.

Scoop out tablespoon-sized dough balls and roll them in the Christmas sprinkles. The dough will be sticky, so after forming the balls, place them on the baking sheet and refrigerate for about 20 minutes to allow the dough to firm up slightly.

Once chilled, bake the cookies for 8-10 minutes or until set. Remove from the oven and quickly press a Hershey's Kiss into the center of each cookie.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.