Mom use to make this for us. I don't have any idea where she got the recipe, but I have had it for many years; we were young when I can remember her making it. She called it a Devil's Float. If you like chocolate and you like "easy", you should try this.
* I should have said that some feel this is best served warm. Actually we eat it as soon as is possible when it comes out of the oven. You can always warm it up in the microwave, but only for seconds so as not to over cook the "cake part". My nephews like it cold, too, though! I have to say, its pretty good that way, too. Hope you enjoy it.
Mix 3/4 Cup of the (white) sugar, four, and 3 Tablespoons of Cocoa. Add milk, then butter and vanilla; beat until smooth. (*I use a whisk. You can use a spoon or whatever you are comfortable with. Do not use a mixer as it puts to much air in the mixture). The batter will be essentially the consistency of a Brownie batter.
Pour into baking dish/pan. Set aside.
In small bowl mix thoroughly the following: 1/2 Cup of the (white) sugar (this is the remaining amount, 4 Tablespoons Cocoa (this is remaining amount), and all the Brown Sugar. Whisk/stir together 'til well blended/mixed.
Sprinkle this mixture evenly over the top of the batter. ***DO NOT STIR***
now gently pour hot water over the top of the mixture. Again-->Do Not Stir!!!
Bake in preheated oven for 35-40 minutes (it may take more time depending on your oven). The top will look dry and will crack. You can check the "cake part" with a tooth pick or cake tester if you need, but do not push tester all the way to the bottom.
This is somewhat like a chocolate cake that makes its own puddin'.