1 cup all-purpose flour
1/3 cup cocoa powder
1/4 tsp. salt
1 stick unsalted butter, softened
2/3 cup sugar
1 egg yolk
2 tbs milk
1 tsp vanilla extract
3/4 to 1 cup assorted Valentine sprinkles
25 to 30 Hershey Kisses, unwrapped
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 and roll each ball in sprinkles, completely covering the dough ball with sprinkles. Place balls about 2 inches apart on a parchment lined baking sheet. With your thumb, gently press down into the center of each ball just slightly to make a very small indentation.
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 in the center of each cookie. Place the cookie sheet in the fridge, that way the kisses won't melt and run everywhere.
Store cookies in an airtight container.