Preheat oven to 350°F.
Place the butter in a 9 x 13-inch baking dish and place it in the oven. Once the butter has melted, remove it and set aside.
Mix together 1 1/2 cups of sugar, 4 tablespoons of cocoa powder, flour, milk, baking powder, salt, and vanilla extract. Pour into a baking dish over the melted butter, but do not mix.
In a separate bowl, mix 2 cups of sugar and 1/2 cup of cocoa powder. Sprinkle the dough into the pan. Pour boiling water over the filling, but again, do not stir.
Bake until the top is done, 35 to 40 minutes. The bottom will be soft and a little slimy.
Allow to cool for 15 minutes before serving.
