Combine cacao, black tea, peppermint tea, and brown sugar and steep in hot water for five minutes.
Meanwhile, heat milk on the stovetop on simmer until little bubbles form on the sides. Makes sure not to let the milk get to a full boil.
Froth warm milk with a electric hand beater. until milk doubles in volume.
Strain out the chocolate mint tea into a mug and top with frothed milk.