In a medium bowl, whisk together All-Purpose Flour (1 cup), Unsweetened Cocoa Powder (1/2 cup) and Salt (1/2 teaspoon).
In a separate bowl (I used my stand mixer) beat Unsalted Butter (1/2 cup) on medium-high speed until smooth, about 1 minute. Add Granulated Sugar (2/3 cup) and continue beating until light and fluffy, about 2 minutes.
Add Egg (1), Whole Milk (2 tablespoon) and Pure Vanilla Extract (1 teaspoon); beat on high speed until combined, about 1 minute. Scrape down sides of bowl as necessary until well blended.
Slowly add in half of flour mixture, beating on low speed just until combined; add remaining flour mixture and continue mixing just until blended. Cover bowl with plastic wrap and refrigerate for at least 4 hours.
Remove cookie dough from fridge 10 minutes before preparing cookies. Preheat oven to 350 degrees F (176 degrees C). Line baking sheets with parchment paper or silpat.
Roll dough into one-inch balls, roll in Sprinkles (3/4 cup). Place 2 inches apart on prepared baking sheets. Bake for 10-11 minutes or until cookies are set.
Remove from oven and immediately place an unwrapped Hershey’s Chocolate Kisses (30) in the center of each cookie while they're still warm.
Transfer to a wire rack and cool completely until Hershey Kiss is set and firm.
Store in airtight container with parchment paper between layers, in a cool location.