400ml Campari
240ml lime juice
Ice cubes, soda water and orange slices to serve

2 bunches rhubarb, trimmed (700gm), thinly sliced diagonally
juice of 1 lemon
500gm caster sugar
1 vanilla bean, split and seeds scraped

For slow-cooked rhubarb syrup, combine ingredients in a heatproof bowl, place over a saucepan of water and stir to combine and until sugar dissolves.
Cover tightly with plastic wrap and cook over low heat until rhubarb is tender and a syrup forms (1.5 hours).
Cool rhubarb in syrup, then strain reserve rhubarb and syrup separately.
Makes about 400ml syrup.

Meanwhile, chill tall glasses. Stir Campari, lime juice and rhubarb syrup in a jug, pour into glasses to taste.
Top up drinks with ice cubes and soda water and garnish with orange slices.