Mix the gin, juice and syrup in a glass. Or be cool and use a cocktail shaker!
Add ice to the glass. if using a shaker, pour the mix over the ice in the glass.
Top with soda water and garnish with mint.
Rhubarb Syrup
Cut up the rhubarb stalks into about 5cm/2" pieces.
Place everything into a small saucepan and bring to boil. Then simmer for 10 minutes, by which time, the rhubarb would be very soft and pulpy.
Strain the syrup into a clean jug, pushing down the rhubarb to extract as much of the flavour as possible. For a clearer syrup, don't squash down, just strain the liquid through.
Leave to cool. Use what you need and keep the rest somewhere cool. A fridge will do too, but the syrup will thicken considerably.
Rhubarb Juice
If using a juicer, just juice the stalk.
If using a chopper, cut up the stalk into 3 pieces and blitz in the chopper.
Strain, squeezing out all the liquid.
Notes
Total time does not take into account the making of the rhubarb syrup and cooling time.