1. Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).
2. Combine flour, sugar, two tablespoons cocoa, baking powder, and salt in a medium-sized bowl.
3. Add milk, oil, and vanilla and whisk together. Spread evenly on bottom of an ungreased 9-inch square pan (if desired, line with Gefen Parchment Paper).
4. Mix brown sugar and the rest of the cocoa and sprinkle over batter. Gently pour hot water over the entire pan. Do not stir!
5. Bake for 35-40 minutes. Serve warm with whipped cream and/or ice cream, and top with ready-made caramel topping, if desired.