Admiral Russell's Punch

In a punch bowl, combine the Demerara (raw) sugar and boiling water. Stir to dissolve. Add the strained lemon and lime juices. Stir more, if needed, to dissolve sugar. Stir in the chilled cognac and chilled sherry or madeira. Add 1 1/2 cups cold water. (Punch can be chilled a few hours at this point; add extra-large ice cubes before serving.) Grate nutmeg over the top and serve garnished with lemon or lime slices.