Mix the butter and sugar.

Add the walnuts, the flour and cocoa.

If you don't have any self-raising flour, add ½ to two-thirds of a teaspoons of Sodium bicarbonate to plain flour.

Add the milk slowly, mixing all the time until smooth.

Mix in the rest of the cocoa and brown sugar, and sprinkle evenly over the mixture, then pour the hot water over it all.

Cook in the microwave for 12 minutes on high (in a 600 Watt oven)

NOTE:
Use a BIG dish as it rises a lot!

from: Di Sinclair.