Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
In medium bowl, whisk together flour, cocoa powder and salt; set aside.
Beat the butter with a mixer on medium-high speed until smooth. With the mixer still running, gradually add sugar and mix until smooth.
Beat in egg yolk, milk/cream and vanilla extract. Gradually add the flour mixture to the creamed mixture until well combined. If dough is dry and crumbly, you add additional milk/cream one tablespoon of milk at a time until dough comes together.
Refrigerate dough for 30 minutes until it is easy to handle and less sticky. Longer chill time will make dough hard to scoop.
Spread sprinkles into a shallow bowl or dish. Use a tablespoon cookie scoop (#60) to portion out dough and roll into a ball with your hands. Roll dough ball in the sprinkles, placing 2 inches apart on the lined baking sheets.
Bake 10-12 minutes; remove from oven and let cool on pans about 3 minutes, then gently press a chocolate kiss candy into the center of each cookie while still warm. Cookies may crack slightly so use a light touch when pressing Kiss in cookie top and press cookie edges back together if this bothers you.
Remove cookies to wire rack to cool completely. Store in airtight container at room temperature. Cookies will stay fresh in an airtight container at room temperature for up to one week.