Pour 1/2 cup milk of choice into saucepan. Sift cocoa powder and sugar into milk. Wisk vigorously to combine until a thick syrup results.
Turn stovetop on to heat medium high heat syrup until just starting to bubble. Add a pinch of salt and optional cinnamon. While whisking, slowly pour in additional 2 cups of milk. Stir occasionally as mixture heats through.
When heated to desired temperature, split into 4 mugs, top with marshmallows, and enjoy!