This ruby-red classic Italian cocktail is pleasantly bitter with a hint of sweetness from the vermouth.
Fill a cocktail shaker or large glass halfway with ice and add the gin, Campari, and vermouth. Using a long-handled spoon, stir for 20 to 30 seconds. Strain into a chilled rocks glass over fresh ice (or a chilled martini glass if you prefer no ice).
Using a vegetable peeler, remove a 3 x 1/2-inch piece of peel from the orange, avoiding the white pith, to create a twist. Twist it over the drink to release a spray of citrus oil, run it around the rim of the glass, and then drop it into the drink. Serve.