Combine Cocoa and Sugar in saucepan. Stir enough milk in to form a smooth paste. Then stir in all but 2 tb of remaining milk. Stir over low heat until the mixture is warm and sugar is dissolved. Pour into shallow pan or ice cube trays. Cover well and freeze for at least 6 hours or overnight. Break frozen mixture into chunks with fork or table knife. Place chunks in food processor bowl fitted with steel blade. Process with remaining 2 tb of milk until no lumps remain and mixture is thick and light in color. Serve at once in frosted goblets as spoon drink, or scrape into bowl, cover and refreeze for at least 8 hours or overnight and serve frozen.
