Prep Dry Ingredients: In a medium bowl, simply whisk together the flour, cocoa powder, and salt until they're well combined. Set this mix aside for a moment.
Cream Wet Ingredients: Grab a large bowl and your electric mixer. Beat the softened butter and sugar together on medium-high speed for about 2 minutes until the mixture looks light and fluffy.
Add Flavor Boost: Now, mix in the egg yolk, milk, and vanilla extract until everything is smooth and perfectly incorporated.
Combine Everything: Reduce your mixer speed to low. Gradually add the dry flour mixture (from step 1) to the wet ingredients. Mix just until the dough comes together – be careful not to overmix!
Chill the Dough: Wrap your chocolate cookie dough in plastic wrap and pop it into the refrigerator for at least 1 hour. This chilling time is super important to make the dough firm and easy to handle.
Get Ready to Bake: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper to prevent sticking.
Shape & Decorate: Take your chilled dough and roll it into cute 1-inch balls. Then, roll each ball generously in the Valentine's sprinkles, making sure it's completely coated.
Indent & Chill (Again!): Place the sprinkle-covered dough balls about 2 inches apart on your prepared baking sheet. Gently press a small indentation into the center of each ball with your thumb. For the best shape, place the entire baking sheet back into the refrigerator for another 10-15 minutes.
Bake Away: Bake the cookies for approximately 12 minutes, or until they look set. They might still feel a little soft when you take them out, but they'll firm up as they cool.
Add the Kiss: As soon as you remove the cookies from the oven, immediately place an unwrapped Hershey Kiss right into the center indentation of each warm cookie.
Cool & Enjoy: Let the cookies cool on the baking sheet for about 3 minutes. Then, carefully transfer them to a wire rack to cool completely. These sweet, festive treats are ready to share!