Add the aged rum (1.5 oz), bourbon (0.5 oz), single malt whisky (0.5 oz), orange curaçao (0.5 oz), demerara syrup (0.25 oz), Angostura bitters (2 dashes) and orange bitters (1 dash) to a mixing glass.

Stir

Fill the mixing glass with large, cold ice cubes. Stir gently with a bar spoon for 30–45 seconds (about 20–30 full turns) until the exterior of the glass feels very cold and the liquid is well diluted and silk-smooth.

Prepare serving glass

Place a single large ice cube in an Old Fashioned/rocks glass. If you prefer slightly more chill, add a few small cubes or cracked ice around it.

Strain

Double-strain the stirred mixture over the large ice cube in the rocks glass using a julep or fine mesh strainer to catch any tiny shards of ice or solids.

Garnish & Finish

Express the oils from an orange twist over the surface of the drink by holding the twist skin-side down about 2–3 inches above the cocktail and giving it a firm squeeze; rub the twist around the glass rim and drop it into the drink.

Optional: Skewer a Luxardo cherry and rest it on the ice or drop it into the drink for a touch of sweetness and presentation.

Serve immediately. Sip slowly to appreciate the layered cask character: rum backbone, bourbon warmth, and whisky finish.