Place a small glass bowl in your freezer.

Stir together red onion and vinegar, and let sit for at least half an hour. In the meantime, use a vegetable peeler (serrated if you have one) to cut strips of peel from the orange, being careful not to remove the white pith. Process in a spice grinder or food processor with some of the sugar. Transfer along with the onion and vinegar to a large, heavy saucepan and add the remaining sugar, vinegar and spices.

Boil over medium heat for about ten minutes, then add the rhubarb and cherries. Simmer until it starts to gel; the rhubarb should be tender but still holding its shape. To test the gel: Take your glass plate from the freezer and transfer a small spoonful of your chutney onto it. Return the plate to the freezer for a few minutes. Take it out and give it a test with your finger to see if it's a bit jelly-like. If it's just liquid, keep cooking and test again in a while.

For consuming within the next couple of weeks, cool the chutney to room temperature then refrigerate for at least an hour.

For water-bath or steam canning, have everything ready (your canner with the hot water started, clean hot jars and screw bands, brand-new jar lids, clean ladle, canning funnel and jar lifter) so that you can ladle hot chutney into your jars. (You can find canning instructions here.) Process for 10 minutes, then let the jars sit in the hot water for another five minutes.