Step 1

In a pitcher or punch bowl, combine Campari, vermouth, and lemon juice; refrigerate until ready to serve (or combine in an airtight container and refrigerate up to 3 days).

Step 2

Just before serving, add ice to pitcher, top with prosecco, and stir once. Pour into ice-filled glasses, top each with a splash of soda, and garnish each with a citrus slice and rosemary sprig; serve immediately.