Beat the yolks and honey at high speed with a whisk attachment until the mixture is very pale and fluffy and thick and a steady ribbon of the mixture flows down from the whisk when it’s lifted from the bowl, about 3 to 4 minutes. Empty the egg yolk mixture into a blender, and add the milk, cream, rum, blackberry liqueur, nutmeg, and cinnamon. Cover and blend at medium speed for 30 seconds. Stir in any froth on top of the mixture and empty into serving vessel. Garnish with a few pinches of nutmeg. Can be served immediately or chilled. Will keep in an airtight container in the refrigerator for up to 2 weeks.