Cream together sugar and butter. Sift together several times: flour, salt, baking powder, 1-1/2 tbls cocoa, milk, walnuts. Add to sugar and butter, alternately with the milk. Pour into a greased cake pan. Sprinkle with nuts. Mix together: brown sugar, white sugar, 4 tbls cocoa. Spread over top of the cake mixture. Pour 1-1/2 cups boiling water over all. Bake at 375~ for about 30 minutes. Cool slightly. Turn upside down.