Add instant coffee, sugar and cocoa powder to a cup and pour 3 tablespoons hot water.
Stir until all the ingredients blend well. Mocha mixture is ready. Set this aside.
Pour 1 cup milk to a sauce pan and begin to heat it until it barely simmers, about 65 C or 130 F. You can also do this in a microwave cup for 1 minute or so.
Pour this to a heat resistant mason jar and seal it tightly. Ensure the milk is not too hot otherwise the jar can explode. Shake the milk to froth up for 40 to 60 seconds. Alternately you may use a milk frother to froth the milk until frothy.
Gently pour the milk from a side to the mocha mixture so all of the froth settles on top. Serve mocha immediately.
Optionally you may top mocha with whipping cream or finely grated chocolate.