Place your Old Fashioned glass in the freezer for a few minutes to get it frosty.
In a mixing glass, add the bourbon, cognac, grenadine, and bitters.
Fill the mixing glass about 3/4 full with ice. Stir for 20 seconds to chill the drink.
Strain the mixture into your chilled glass. Express the oils of a fresh lemon twist over the surface of the drink, rub it along the rim, and drop it into the glass.