In ungreased 9 x 9 inch square pan stir together flour, sugar, 2 Tablespoons cocoa, baking powder and salt. Mix in milk, oil, and vanilla with fork until smooth. Stir in nuts.
Spread evenly in pan. Sprinkle with brown sugar and 1/4 cup cocoa. Pour hot water over batter. Bake 40 minutes.
Let stand 15 minutes; cut into squares. Invert each square onto dessert plate. Top with ice cream and spoon sauce over each serving.
