1) Combine together the cocoa, sugar, cosntarch and coffee powder in a saucepan.
2) Stir in the milk slowly.
3) Cook the mixture, constantly stirring, till it is thick and bubbly.
4) Take the mixture off the heat and add the vanilla. Stir well.
5) Spoon the warm Mocha Sauce over ice cream and serve. Can also be used as a topping for various desserts like cakes and muffins.