Preheat oven to 350°F. Line at least two baking sheets with parchment and set aside.
Combine flour, cocoa powder and salt in a medium bowl. In the bowl of an electric mixer, beat the butter on medium-high speed until smooth. With the mixer still running, gradually add sugar and mix until smooth. Beat in egg yolk, milk or cream and vanilla extract. Gradually add the flour mixture to the creamed mixture until well combined. Refrigerate dough for at least 30 minutes until it is easy to handle, and less sticky.
Spread sprinkles into a shallow bowl or dish. Shape dough into portions the size of a small walnut and roll in the sprinkles, them place 2 inches apart on the lined baking sheets. Bake 10-12 minutes; remove from oven and let cool on pans about 3 minutes, then lightly press a chocolate kiss candy into the center of each cookie while they are still warm. Remove to wire racks to cool completely.
Cookies will stay fresh in an airtight container at room temperature for up to one week.
What to expect: This recipe yields 20-22 cookies. Using a heaping tablespoon, you'll average about 18 cookies. Using a small cookie scoop, you'll get about 20-22.