1⁄4 cup/50 g granulated sugar (CP Note: Or try alternative sugars, like coconut sugar)
2 vanilla beans
Preheat the oven to 350°F/180°C.
Wash the rhubarb and chop into 2-inch/5 cm lengths.
Arrange the rhubarb pieces in the bottom of an oven-safe baking dish. Put the sugar in a small mixing bowl. Scrape the vanilla bean seeds from the pods and add it to the sugar.
Using a fine rasp, grate the lemon zest into the sugar. Toss the sugar, vanilla seeds, and lemon zest together and sprinkle over the rhubarb pieces. Cut the lemon in half and squeeze the juice from one half over the rhubarb.
Place the baking dish in the preheated oven and roast for 20 to 25 minutes, until the rhubarb pieces are quite tender but have not lost their shape. When they’re done, their color will have faded into a dusky pink.
While the rhubarb roasts, prepare a boiling water bath and sterilize 2 half-pint/250 ml jars. Place 2 lids in a small saucepan of water and bring to a gentle simmer.
Scoop the roasted rhubarb into the prepared jars. Wipe the rims, apply the lids and rings and process in a boiling water bath for 10 minutes.