1/2 cup ice, or as needed
1 fluid ounce gin
1 fluid ounce bitter orange aperitif (such as Campari®)
1 fluid ounce sweet vermouth
1 fluid ounce simple syrup
1 (1×2-inch) orange peel
Fill a chilled cocktail shaker 3/4-full with ice; add gin, orange aperitif, vermouth, and simple syrup and stir. Strain drink into a martini glass.
Squeeze the orange peel over the drink and drop into the glass.