Preheat the oven to 375 degrees F and line baking sheets with parchment paper.
Cream the butter, sugar, and brown sugar together on medium high speed for 3 to 5 minutes, or until fluffy and very pale.
Beat in the egg on medium high speed, until completely incorporated.
Scrape the bottom and sides of the bowl with a silicone spatula, then add the milk and vanilla, mixing on medium-high speed until smooth.
Add the flour, cocoa powder, baking soda, and salt, and mix on medium speed until well-blended.
Use a 1.5-tablespoon cookie scoop to portion out the dough. Roll between your palms to make a smooth ball.
Lightly press the bottoms and sides of the balls into the sprinkles, and transfer to the prepared baking sheets.
Bake for 8 to 10 minutes, or until puffed and set around the edges but still soft in the middle.
Press a Dove® Milk Chocolate Promise into the center of each warm cookie.
Cool completely, then package in treat boxes and gift with an American Greetings® card.