Sift flour, salt and cocoa powder into a bowl and stir in the raw sugar. Add the milk, melted butter and vanilla essence. Mix with a wooden spoon until smooth. Add nuts and stir through. Spoon the mixture into a six-cup capacity ovenproof dish.
Mix the brown sugar and extra cocoa powder together and sprinkle over the cake mixture.
Carefully pour the hot water in at the side. Bake for 45 minutes then let stand for about 5 minutes.
Scoop into bowls with plenty of sauce and serve with vanilla ice-cream.