Preheat oven to 350°F (180°C).
Combine the flour, bran, walnuts, sugar, baking powder, 2 tbsp. cocoa powder and salt in a bowl. Stir in milk, vegetable oil and vanilla. Pour batter into a greased 8 x 8” (2 L) baking dish.
In a small bowl stir together brown sugar and 3 tbsp. cocoa powder. Sprinkle mixture over batter. Pour hot water over entire mixture. DO NOT STIR. Bake for 45 minutes or until done. Serve warm with whipped cream or ice cream.