Bitter and aromatic gentian root—a key component of Angostura bitters, and here infused in orange vodka—is one of Francesco Lafranconi's favorite cocktail ingredients. It's sold at health-food stores. More Vodka Drinks
Fill a pint glass with ice. Add all of the remaining ingredients except the garnish and stir well. Strain into a chilled coupe and garnish with the grapefruit twist.