This syrup, used in Rhubarb Fizz, is also delicious in lemonade or straight Prosecco, folded into whipped cream, or over ice cream.
Combine sugar, water, vanilla pod and seeds, and rhubarb in a medium saucepan and bring to a boil, stirring to dissolve sugar. Simmer until rhubarb is tender, about 3 minutes. Let cool completely. Remove vanilla pod before serving, if desired.