Combine all ingredients in a blender or a food processor and blend until smooth, scraping down the sides in between. Add more milk if needed to help blend.
Taste test it to see if you prefer more chocolate flavor (add more cocoa powder, 1 tablespoon at a time), more sweetness (add a splash of maple syrup) or more vanilla. Blend until smooth.
Transfer to an airtight container for storing. Refrigerate for up to 4 days. Serve chilled adding a whipped topping or nuts as desired.