Start by placing your old-fashioned glass in the refrigerator or freezer for at least 5 minutes so it’s nicely chilled.
In a mixing glass or shaker, add the gin, Campari, and sweet vermouth. Fill the glass about halfway with ice.
Stir gently for about 30 seconds, until the drink is very cold and well balanced.
Strain the cocktail into your chilled glass. You can serve it over fresh ice if you like.
Twist a wide strip of orange peel over the drink to release the oils, then drop it in as a garnish. Sip and enjoy.