In saucepan mix cocoa and sugar
Whisk in 1/2 a cup of milk. Gradually whisk in the rest of the milk. Bring to a boil, reduce heat and simmer 5 minutes.
Transfer liquid to a 9x13" baking pan and freeze 1-2 hours (till slushy).
Break up mixture with a fork and freeze 2 hours longer, stirring eery 30 minutes.
Break up mixture and transfer to a food processor or blender with t TBS water. Mix till smooth.
Pour into glasses & top with whipped cream.