Mix graham cracker crumbs with 2 tablespoons melted butter, press into 6-inch cast iron pan or small baking pan.
Combine 1/3 cup granulated sugar, flour, 2 tablespoons cocoa powder, baking powder and salt. Stir in milk, 3 tablespoons melted butter and vanilla. Beat until smooth and pour on top of graham cracker crumbs.
In another bowl mix brown sugar, 1 tablespoon of cocoa powder and sprinkle over batter. Pour hot water on top, do not stir.
Bake for 18-20 minutes at 350° F until center is still jiggly. Add marshmallows and burn with torch until golden brown. Remove and let stand for 5 minutes.