Combine flour, baking powder, salt, cocoa, and sugar.
Sift into a mixing bowl.
Add milk, nuts, butter, and vanilla; blend well.
Pour into a well-greased, 9-inch square metal pan or flameproof baking dish.
Prepare Chocolate topping and spread evenly over batter.
Slowly pour boiling water over all do not stir.
Bank 20 low-glowing coals on each side of fire grill.
Place cooking grill 4 to 6 inches above coals.
Place baking pan in center of grill so that no part is directly over coals.
Cover barbecue and adjust dampers according to manufacturer's directions.
Cook for about 45 minutes and then test for doneness.
Pudding should be slightly crusty on top and firm.
Continue checking every 5 minutes until desired doneness is reached.
Spoon into individual dishes and top with whipped cream or ice cream, if desired.