Take two old-fashioned glasses. Chill one with crushed ice. In the other: muddle the sugar cube, water, and bitters. Add the bourbon (or brandy if you want another 1850's version) and stir.
Dump the ice from the first glass and pour enough of the Herbsaint to coat the inside of the glass (a wash). Swirl it around, then dump the rest. Add new ice and the contents of the second glass. Finally twist a lemon peel over it, but don't add it to the drink.