Combine flour, cocoa, and salt; set aside.

With an electric mixer on medium-high speed, beat butter and sugar until light and fluffy, about 2 minutes. Add egg yolk, milk, and vanilla; mix until incorporated. Reduce mixer speed to low and add the flour mixture until just combined.

Wrap dough in plastic wrap and refrigerate until firm, 1 hour.

Roll chilled dough into 1-inch balls. Place balls about 2 inches apart on a baking sheet. Chill the baking sheet of dough balls in the refrigerator for 10 to 15 minutes.

Bake at 350 degrees until set, about 12 minutes.

After removing cookies from the oven, immediately place a Hershey Kiss or Dove Chocolates in the center of each cookie. Let cookies cool on the baking sheet for about 3 minutes, remove to a cooling rack to cool.

Makes approximately 25 to 30 cookies.