Rhubarb and custard soda

Method

1. Put the rhubarb in a saucepan with 200ml water. Bring to a simmer over a medium heat, then cook for 10 minutes.
2. Line a sieve with muslin or kitchen paper, then set over a jug or bowl. Pour the contents of the pan into the sieve. Leave until the liquid stops dripping into the bowl.
3. Gather up the muslin or paper and give it a squeeze to extract any remaining liquid from the solids. Pour the liquid back into the pan, add the sugar and simmer briefly (1-2 minutes) until the sugar has dissolved. Stir in the vanilla bean paste, then leave to cool.
4. Decant the syrup into a bottle or container and keep in the fridge until needed (see Make Ahead). To serve, add a splash to a glass filled with ice and top up with soda water.