Carefully remove the corn from the cob, and blend it with the water in a blender.
Pass the mixture through a sieve and discard the pomace.
Bring the sifted mixture to a boil, add the milk and mix. Add the butter and condensed milk, and mix constantly with the help of a fouet (wire whisk), so it doesn't stick to the bottom of the pan and burn.
Place in a bowl or individual bowls and sprinkle with cocoa powder. Serve warm or chilled.