Fill an Old Fashioned glass with cubed ice. In a second glass, crush together the sugar cube and Peychaud’s Bitters. Add the Whiskey, fill with ice and stir. Empty the ice from the first glass and coat the glass with Herbsaint, then discard remaining Herbsaint. Using a strainer, pour the mixture from the second glass into the chilled Old Fashioned glass. Garnish with lemon peel.