01 -
In a saucepan, combine chopped rhubarb, sugar, and water. Bring to a boil over medium-high heat, then reduce to a simmer and cook for 20 minutes.
02 -
Remove saucepan from heat and allow to cool completely. Strain the mixture through a fine-mesh sieve, discarding the rhubarb solids or reserving for another use.
03 -
Fill two chilled highball glasses halfway with ice. Add 60 ml gin and half the lime juice to each glass.
04 -
Pour 90 ml rhubarb simple syrup into each glass. Top up with 150 ml chilled tonic water per glass.
05 -
Garnish each glass with fresh lime slices and serve immediately.