In a saucepan, whisk 1 1/2 cups of milk with the cocoa and carob powders, sugar, and salt until smooth.
Place the saucepan on the stove, and turn the heat to medium high.
In a separate bowl, whisk together the remaining 1/2 cup of milk and the tapioca starch.
Heat the cocoa mix until steaming.
Whisk in the tapioca slurry and keep stirring until thick (3-5 minutes).
Once thickened, remove pan from heat.
Stir in vanilla and stevia.
Serve hot with marshmallows and/or whipped cream!