Add the black cocoa powder and finely chopped chocolate to a coffee mug, and brew the espresso directly over it. Mix the chocolate and espresso together until the chocolate has melted.
Add in the milk and ice.
Make the dark chocolate cold foam. Add the milk, heavy cream, sugar, and cocoa powder to a medium sized cup or container. Froth or shake the mixture until it's thick and foamy.
Top the drink off with the dark chocolate cold foam.
(Optional) Use a Halloween stencil to create a design on top of the mocha. Dust first with cocoa powder, then powdered sugar. Serve and enjoy!