Preheat oven to 350°F. In a medium bowl, whisk together flour, baking powder, salt, sugar and cocoa powder. Create a well in dry ingredients and pour in milk, melted butter and vanilla. Stir together until a thick batter forms. Pour into a small, ungreased, rectangular casserole dish with high sides.

In a separate bowl, stir sugar, brown sugar and cocoa powder together. Sprinkle over top of batter. Pour hot water over entire pan. Do not stir. Place pan on a baking sheet in case it bubbles over. Bake 40 minutes or until middle is set. Cool 5-10 minutes before serving. Serve warm with vanilla ice cream.