First you will need to create the Rhubarb simple syrup. It's very easy: chop one and a half cup of rhubarb, add one cup of sugar and one cup of water. Boil until the waters looks syrupy, drain on a mason jar. Reserve in the fridge (it lasts up to 3 weeks!) This makes about one cup of syrup, multiply the measurements to make more if you are expecting to make lots of mojitos.