A bold, strong cocktail with both high-proof bourbon and light rum gets a hit of floral sweetness from mellow crème de banane.
Fill a tall mixing glass with ice cubes. Add bourbon, rum, crème de banane, and bitters. Stir for 5 seconds; strain into a rocks glass over a large ice cube. Twist orange peel strip over cocktail to express oils; tuck orange peel into glass, or discard.
Batch this cocktail by combining bourbon, rum, crème de banane, and bitters in a pitcher; stir in ice just before serving.