Puree the banana, milk, cocoa powder, peanut butter, and honey in a blender. Taste and add more sweetener if desired.
To cut down on the calories and fat, I prefer using peanut butter powder in this recipe. The nutritional info in this recipe references regular peanut butter. For added protein, I almost always add Vital Proteins Collagen Peptides. Please not that this is not a vegetarian protein powder, but is completely flavorless.
If you want to add additional sweetness without using honey or agave nectar, you can add 1/2 a chopped apple (I don't bother peeling it, but you might want to since the peel adds some texture). Another option would be a few drops of liquid Stevia.