In a mixing glass, combine the bourbon whiskey, dry vermouth, and aromatic bitters.

Add ice to the mixing glass until it is about three-quarters full.

Stir the mixture gently for about 30 seconds to chill and dilute the cocktail without making it too watery.

Strain the cocktail into a chilled martini glass or a rocks glass if you prefer it on the rocks.

Garnish with a lemon twist or a cherry, depending on your preference.