In a 9 x 13-inch baking dish, place the butter and let it melt in the oven. Set aside once melted.
In a mixing bowl, place the 1 1/2 c. sugar, 4 tbsp cocoa powder, flour, milk, baking powder, salt, and vanilla extract. Mix well until blended. On top of the melted butter, spoon the mixture. DO NOT STIR.
Whisk 2 c. sugar with half c. cocoa powder in another bowl. Sprinkle this on top of the batter. Over the topping, pour boiling water. DO NOT STIR.
Place in the preheated oven and bake for about 35 to 40 minutes or until the top of the cobbler is set and the bottom is loose and slightly gooey.
Before serving, let the cobbler cool for about 15 minutes.
Notes
How To Make it Gluten-free:Substitute all-purpose flour with gluten-free flour.