Line a cookie sheet with parchment paper or a Silpat and set aside. (You can skip this step, but it just makes the cookies easier to remove from the cookie sheet.)
Whisk together flour, baking powder and salt in a medium bowl and set aside.
In the bowl of a stand mixer or a large bowl with a hand mixer, add butter and shortening.
Beat butter and shortening on medium speed until creamy.
Add sugar to the bowl with the butter and shortening.
Mix on medium speed until light and fluffy.
Add egg yolk and mix until just combined.
Add vanilla extract and mix until just combined. Scrape down bowl with a rubber spatula when needed.
Add milk and mix until just combined.
Add flour mixture to bowl and mix until just combined. Scrape down bowl as needed.
Chill dough in the refrigerator for at least an hour.
Unwrap the chocolates and set them aside.
Preheat oven to 350° F.
Using a cookie scooper or tablespoon to help with the size, roll out balls of dough and dip into colored sugar and place on the prepared cookie sheet about 2 inches apart. I'm able to fit a dozen cookies onto one cookie sheet.
Bake cookies for 9 minutes and then remove from the oven.
Press a chocolate heart into the center of each cookie.
Return cookies to the oven for 1 minute.
Remove cookies from the oven and transfer to a cooling grid until cool.
Enjoy!