Fill a rocks glass with ice; set aside to chill, about 5 minutes. Discard ice.
STEP 2
In a shaker, place Peychaud's Bitters, Angostura Bitters, and a sugar cube. Mash well with a muddler. Add more ice and whiskey; stir until chilled. Strain into the chilled glass.
STEP 3
Twist lemon peel over cocktail surface to extract essence; discard lemon peel.