Rhubarb and Campari Spritzer

1.For slow-cooked rhubarb syrup, combine ingredients in a heatproof bowl, place over a saucepan of simmering 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 (1½ hours). Cool rhubarb in syrup, then strain reserve syrup and rhubarb separately. Makes about 400ml syrup. Reserved rhubarb can be used as an accompaniment to the cheese and olive oil, chestnut and rosemary biscuits.

2.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.