Add your milk, pumpkin puree, brown sugar, vanilla, and all the spices into a small saucepan. Whisk everything together until it looks smooth and fully combined, with no lumps of pumpkin left floating around.
Place the saucepan over medium-low heat and let it warm slowly, whisking occasionally so nothing scorches on the bottom. You'll know it's ready for the next step once small bubbles start forming around the edges of the pan.
Lower the heat to low and add your chopped chocolate directly into the warm milk mixture. Stir continuously until the chocolate has fully melted, turned glossy, and thickened slightly, which usually takes about one to two minutes.
Once the mixture is smooth and hot, pour it carefully into your favorite mug. Top it with a spoonful of lightly sweetened whipped cream and a dusting of cinnamon for that finished, coffee-shop look.
This drink is best enjoyed right away while it's still steaming hot and the whipped cream is just starting to melt into the surface. Grab a spoon if you like scooping up that first bit of cream before you sip.