Preheat the oven to 180C.
Make the sauce by putting the cocoa and sugar into a small bowl and using a wooden spoon mix in a little of the hot water to make a smooth paste.
Gradually mix in the rest of the hot water.
Grease a 1 litre oven-proof dish.
Place the dish on a baking sheet.
Put all the pudding ingredients into a mixing bowl and beat together with a wooden spoon until smooth.
Scrape the pudding mixture into the dish, and pour the sauce mixture over the top.
Place the dish (still on the baking tray) on the middle shelf of the oven.
Bake for 15-20 minutes until the pudding is well risen.
Serve with vanilla ice cream or cream.