Fill a cocktail shaker about three-quarters full of ice and add the rye, vermouth and bitters. Stir with a bar spoon until the contents are ice cold.
Strain liquid into two cocktail glasses and garnish each with a lemon twist.
Notes
Shaken or stirred? For this cocktail I love the chill of shaken but the look of stirred. So I put my glasses in the freezer for about 10 minutes before making the cocktail and then I stir the ingredients with some medium size ice chips. If you prefer a more icy composition, then shake away but the clarity of the cocktail can be affected.