1. Blend cocoa and sugar to a smooth paste with a little of the cold milk.
2. Heat the remaining milk in a small saucepan; add hot milk to the blended cocoa.
3. Rinse pan; pour in cocoa. Heat the cocoa gently, stirring at the same time until it boils. Allow the cocoa to cook gently foe 1/2-1 min.
4. Pouur straight into a cup, or into a serving jug.