When I need a chocolate fix (which is pretty much every day) I make something along the same lines. I have an old Nutella jar in the fridge which contains a blend of melted butter, vanilla paste, water and cocoa. I mix a dollop of this into some full fat yogurt and eat it with a teaspoon to make it last as long as possible. It hits the spot every time. I also freeze the chocolatey yogurt in an ice-cube tray and blitz the cubes to make an ice-cream style treat. This comes in at c80 calories (per 1/2 cup portion) and contains minimal carbs. Jobs a goodun!
Edit: I also add a bit of Stevia...of course.