Once frozen, remove the pan from the freezer. Hold on to two sides of the parchment to lift the cream out of the pan and set it on your work surface. Press a heart-shaped cookie cutter into the cream, and use your finger to gently and slowly press it out of the cookie cutter. Cut out as many hearts as will fit. Work quickly, because the cream melts! Store the hearts in a single layer in a covered container in the freezer until ready to use. If any of the hearts crack along the way, piece them back together and refreeze.
Put the milk, cocoa powder, and remaining sugar in a small saucepan and set over medium-high heat. Whisk vigorously to incorporate the cocoa powder and sugar into the milk. Once the cocoa powder is mixed in, stir occasionally until the cocoa is warmed to your liking, being sure that the sugar dissolves. Add the vanilla and stir again.