Chill your wine glass or spritz glass in the freezer for 5 minutes, or fill it with cold water while you gather everything else.
Fill the chilled glass with ice cubes right to the rim.
Measure 60 ml / 2 oz Cynar and pour it directly over the ice.
Add 90 ml / 3 oz chilled prosecco, pouring slowly down the inside of the glass to keep the bubbles.
Top with 30 ml / 1 oz chilled soda water.
Stir once, gently, with a bar spoon to combine without knocking out the fizz.
Slide in an orange slice and a mint sprig if using. Serve right away while it's cold and lively.