In an ungreased square pan, 9" X 9" X 2", stir together flour, sugar, 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 for 40 minutes. Let stand for 15 minutes.
Spoon into dessert dishes or cut into squares, then invert each square onto dessert plate.
Top with ice cream and spoon sauce over each square.