Mix Bisquick, half cup sugar, 3 tablespoon cocoa, milk and vanilla. Spoon batter evenly into greased crockpot. Mix remaining sugar, cocoa and hot water. Pour over batter in crockpot. Cook on high 2 to 2.5 hours, or until batter no longer looks shiny on top. Don't overcook.
The batter rises to the top like cake, underneath is a rich chocolate pudding. Serve with ice cream or whipped cream.