In a bowl, combine butter, 0.5 cup granulated sugar, and the vanilla.
Mix flour, 3 tablespoons cocoa, instant coffee, baking powder and 1/2 teaspoon salt.
Add alternately with milk, to the first mixture, stirring until well blended. Add nuts.
In a 1.5 litre baking dish, combine remaining granulated sugar, cocoa, salt and 1-2/3 cups of boiling water.
Drop batter tablespoonful onto boiling mixture (stand dish over low flame to keep liquid boiling).
Bake in moderate oven oven at 180 degrees C/350 degrees F. Sprinkle confectioners' sugar and while still warm, spoon out portion of pudding and cover with sauce.
To Serve : Top each serving with whipped cream, if desired, to which a drop of sugar mill rum may be added.