3 heaping spoonfuls sugar
1 heaping spoonful dutch-process cocoa powder
scant 1/8 tsp salt (a pinch)
1/8 tsp cinnamon (a generous pinch)
very tiny pinch (just a few grains) chili powder
1/8 tsp vanilla extract (the real thing, not that nasty imitation stuff)
~1 Tbsp water (just eyeball it)
~1 1/2 C milk (again, eyeball it, depending on the size of your mug)
In the bottom of your cocoa mug, combine the sugar, cocoa powder, salt, cinnamon, & chili powder. Mix them thoroughly so that they are uniformly combined- the cocoa powder will want to stay separate in the bottom of the mug. Add the vanilla and just enough cold water to stir the dry ingredients into a thick slurry, again being sure to incorporate all the cocoa powder. Add the cold milk but do not stir. Heat the mug in the microwave until piping hot (60-90 seconds, depending on your microwave), and then stir. For extra points, sprinkle the top with chocolate shavings or mini marshmallows, or top with whipped cream.
If you find yourself making cocoa often, it may be worthwhile to mix up a larger batch of just the dry ingredients, using the same proportions, so that you need only add the water, vanilla, & milk whenever you need a warm, chocolaty cuppa.