Preheat the oven to 350 degrees F. Line baking sheets with parchment paper or Silpat baking mats and set aside.
In a medium bowl, whisk together the flour, cocoa, and salt. Set aside.
In the bowl of a stand mixer or using a handheld mixer, beat the butter on medium-high speed until smooth, about 1 minute. Add the sugar and beat on medium-high speed until creamed, about 2 minutes. Add the egg yolk, milk, and vanilla extract, and beat on high speed until combined, about 1 minute. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine.
Add the dry ingredients to the wet ingredients and mix on low speed until combined.
Pour the sprinkles into a small bowl. Roll the balls of dough, about 3 teaspoons of dough per cookie, then roll each ball into the sprinkles to coat. Place the dough balls on the prepared baking sheet, 2 inches apart.
Bake the cookies for 9-12 minutes. Check early to be safe. You want to take them out when they are still soft in the center.
Remove the cookies from the oven and allow them to cool on the baking sheet for 5 minutes. Press the chocolate kisses into the center of each cookie. Transfer the cookies to a wire rack to cool completely.
Note-cookies will keep in an airtight container at room temperature for up to 1 week.