In the bowl of your stand mixer (or a large mixing bowl), add the softened butter and sugar and beat on medium until light and fluffy.
Add in the milk, vanilla, and egg and blend well.
Add in the flour, cocoa powder, baking powder, and baking soda. Stir to blend well.
CHILL FOR APPROX. 1 HOUR so it's easier to work with.
Once chilled, preheat the oven to 350 degrees and line two baking sheets with parchment paper or silicone baking mats. Set aside.
Flour your clean surface (I like to use a large cutting board) and roll out 1/3 of your dough to about 1/8 thick.
Flour your cookie cutters and cut out the hearts then place them on the prepared baking sheets, about 1" apart. I made various sizes and cut out the centers of some of the cookies. Repeat until out of dough.
Bake for 9-10 minutes or until just set.
Remove from oven and immediately transfer to a cooling rack to completely cool.
Once completely cool, frost and sprinkle.