Sift together flour, sugar, 3 Tablespoons cocoa, baking powder and salt into mixing bowl. Add milk, oil and vanilla; blend 1 minute, using an electric mixer at medium speed. Pour mixture into greased 9-inch square baking pan. Combine 1/4 cup cocoa and brown sugar. Sprinkle over batter. Then add the nuts. Pour the hot water evenly over all. Bake at 350*F for 45 minutes or until toothpick inserted in cake part, comes out clean. Serve warm.