Preheat oven to 350F.
Dry Ingredients: In a medium-sized bowl, whisk together flour, baking powder, salt, sugar and cocoa powder.
Mix Wet Ingredients: In a glass, mix milk, butter and vanilla extract.
Add Wet Ingredients: Create a well in the dry ingredients and pour the wet ingredients mixture. Stir together until a thick batter forms. Pour into a small, un-greased 6-inch dish with high sides.
Make the Hot Fudge: In a separate bowl, stir sugar, brown sugar and cocoa powder together. Use your fingers to mix to make sure there are no lumps in the brown sugar.
Sprinkle Hot Fudge Mixture: Sprinkle over the top of the batter evenly. Pour hot water all over the top DO NOT STIR. Be sure to place on a baking sheet in case it bubbles over.
Bake: 17 minutes or once the middle is set and top is almost dry and starts to crack. Cool 5-10 minutes before serving. Serve warm with vanilla ice cream or whipped cream.