I normally never drink cordial, but a home made rhubarb cordial is something I can down in a sec! I prefer to make my own;
1 kg of trimmed washed rhubarbs, that you chop into smaller pieces.
That you boil until soft ,then drain them over a bowl or a jug with a piece of muslin, or a clean tea towel. It takes around 1-2 hours. Squeeze out everything!
Add 2-3 dl white granulated sugar and boil until the sugar has dissolved. Add some water , and fill up into a nice clean bottle.
You can add some lemon or ginger if you want;)
1 kg Rhubarbs
2-3 dl White Granulated sugar
Lemon or ginger, if you want