Whisk all ingredients together in a bowl and then add to a saucepan over low to medium heat. Continue to whisk to allow a gentle foam to develop. Allow to warm to your desired heat. Serve topped with a light dash of cacao/cocoa.
Tip: If you have a sweet tooth then try sprinkling 1/4 of a tsp of sugar over the top of the drink once poured. This way, you drink a small amount of sweet liquid with every mouthful which can make the drink feel more heavily sweetened than it is. This trick also works for children.
For particularly sugar-addicted kids (or adults) as a rule of thumb, start with a sweetened recipe to gain 'trust' in the recipe. Then gradually reduce the sugar each time you make it until you find the lowest level that is tolerated. This often results in enjoying a much lower level of sweetness in just days to weeks.