Add all ingredients to a blender.
Blend on medium speed until the mixture is very smooth; you may need to stop and scrape down the sides of the blender a few times.
If the mixture is too thick, add a small amount of milk to help with blending, if necessary.
Refrigerate for at least 30 minutes to allow the mixture to firm up further.
Top with whipped cream or yogurt and garnish with shaved chocolate.