Fill mixing glass with ice. Add gin, sweet vermouth, Campari, cardamom syrup, and orange bitters.
Stir gently for 25–30 seconds until well chilled.
Strain into a rocks glass over a large ice cube.
Express orange peel over the drink and drop it in for garnish.
Notes
Homemade cardamom syrup: Simmer cardamom pods with sugar and water. Adjust syrup for sweetness. Try a barrel-aged gin for more depth, or add a splash of soda water for a lighter style.