Chill a highball glass in the freezer for 5 minutes if you have time.
Juice 2 medium oranges to get about 90 ml of fresh orange juice.
Froth the orange juice alone using a milk frother, small blender, or by shaking hard in a tight-lidded jar for 15 seconds, until it turns pale and foamy on top.
Fill the chilled glass with ice cubes.
Pour 45 ml of Campari over the ice.
Slowly pour the frothed orange juice on top so the foam sits above the Campari.
Give it one gentle stir with a bar spoon, just enough to combine without killing the foam.
Garnish with an orange wheel and serve right away.