Place butter in dish, melt in microwave on high 1 minute, stir in sifted flour, sugar and cocoa, milk and vanilla, beat until smooth with wooden spoon.
Sprinkle with combined sifted brown sugar and extra cocoa. Pour boiling water over mixture carefully. Divide into cups.
Cook on HIGH for 12 minutes, or until just cooked in centre; stand 5 minutes before serving with cream or ice-cream.