Mix flour, granulated sugar, 2 tablespoons cocoa, the baking powder and salt in medium bowl. Mix in milk, oil and vanilla with fork until smooth. Stir in nuts. Spread in ungreased square pan, 9x9x2 inches.
Sprinkle brown sugar and 1/4 cup cocoa over batter. Pour water evenly over batter.
Bake about 40 minutes or until top is dry. Cool 10 minutes.
Spoon warm cake into dessert dishes. Top with ice cream. spoon sauce from pan onto each serving.