Getting the Challenge Cocoa Brownies brought me in contact with other box-side recipes, such as this one from Hershy's. You'd think they'd know a thing or two about cocoa.
Their website (http://www.hershykitchens.com) is some serious mojo, best visited after near-complete satiation.
In a saucepan, mix water, sugar, cocoa and salt. Bring to a boil and stir at boil for two minutes. Stir in milk and bring to heat but do not boil.