Place the serving glass (rocks or coupe) in the freezer or fill it with ice water while you prepare the cocktail to chill it. Leave to chill for at least 3–5 minutes.

Combine ingredients

Add the bourbon, dry vermouth, sweet vermouth, orange curaçao, Angostura bitters, orange bitters, and simple syrup (if using) into a mixing glass.

Add ice and stir

Fill the mixing glass with large ice cubes. Using a bar spoon, stir the mixture briskly but smoothly for 20–30 seconds (about 15–20 full rotations) until well chilled and slightly diluted. Proper dilution should be around 20–25% total dilution by weight—stir until the mixing glass feels very cold to the touch.

Strain

Discard ice or water from the chilled serving glass. Using a Hawthorne or julep strainer, strain the cocktail from the mixing glass into the chilled serving glass. If you prefer the cocktail over a single large ice cube, add one large clear ice cube to the rocks glass before straining.

Express and garnish

Take an orange peel and hold it over the drink with the exterior skin facing down. Give it a quick squeeze to express oils over the surface, then rub the peel along the rim and drop it into the drink as garnish.

Serve

Present immediately. Sip slowly to appreciate the balance of whiskey, vermouths, and citrus-vanilla notes from curaçao and bitters.

Tools

Use the mixing glass, bar spoon, and strainer to build and chill the cocktail as described above. Chill the serving glass ahead of time and use a peeler or channel knife to make a clean orange twist for garnish.