Swirl the chocolate inside your glass by laying the glass on its side and turning it. Set it upright again. The swirls will run down, which is the right look.
Put the ice cream and alcohol in a blender, keeping everything as cold as possible. Blend until smooth.
Pour into prepared serving glass. Top with whipped cream and chocolate shavings if desired.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.