Sprinkle the sugar in a pan. Melt the sugar on temperate heat until dark red. Add water, the sugar will steam and hiss and become hard. Then add the rest of the milk. Sir with a wooden spoon until the caramel has dissolved. Pour in the custard powder/milk paste, and whisk until the custard has thickened. Take it off the fire, and add the still hot coffee. The coffee must not boil. Whisk until the custard is smooth again and immediately pour the custard into a bowl. Cover with plastic foil and let it cool.