Pour the bourbon, sweet vermouth, and Campari into a cocktail shaker filled with ice. Shake well, then strain into a chilled rocks glass with an ice cube or two in it.
Garnish with the orange peel (give it a good twist over the glass before dropping it in), and add the cherry.
Notes
A Boulevardier is usually served on the rocks, preferably with one nice big ice cube. You could also serve it neat or straight up, as long as it was well chilled first, but most of us like our drink to stay cold as we slowly sip it.