Preheat oven to 350°F and grease an 8x8 baking dish.
Mix flour, sugar, cocoa, baking powder, salt in a bowl.
Add milk, butter, vanilla and stir until combined.
Spread batter evenly in baking dish.
Mix brown sugar, cocoa and granulated sugar for topping and sprinkle over.
Pour hot water over the topping; do not stir.
Bake 35–40 minutes until top is set and center is jiggly.
Let it rest 5–10 minutes before serving warm.