Add ice to a tumbler.
Pour the sweet vermouth, Campari, and prosecco and stir gently to blend the flavours and squeeze the orange peel over the drink to infuse with citrus oils.
(Pouring the prosecco down a bar or long spoon that’s been placed in the glass will stop the bubbles spilling over the edge of the glass.)
Rub the outside of the peel on the glass rim, twist, and add to the glass.
