Rhubarb Jam

The next recipe in our cookbook requires rhubarb jam, and I couldn't get any at the shops. Fortunately, it's summer, and rhubarb is in season, so I bought some from the supermarket to make a traditional rhubarb jam. Rhubarb Jam Rhubarb Sugar Lemon (1 per kg rhubarb) optional: 1 pinch salt per lemon Slice rhubarb and weigh it. Measure out an equal amount of sugar by weight. Slice lemon(s). Layer rhubarb, sugar, salt (if using), and lemon slices in a container and put in fridge for minimum 24 hours, up to two weeks. Remove from fridge, and allow to come to room temperature. Remove all lemon slices except two per kg of rhubarb. Put all into a pot, and gently bring up to a boil. Cook until rhubarb is soft, sugar is completely dissolved, and temperature is 104 degrees C (220F), or until jam shows signs of setting using the spoon method or freezer-cold plate method. Remove the remains of the lemon slices, blend with an immersion blender if you require a smooth jam. Pour into jars and either freeze, store in refrigerator, or waterbath can to be shelf-stable. Please note that this is not an "approved" canning recipe. I believe that it is safe, but may not last as long once opened, compared to the approved recipes. An approved recipe is available here: https://www.bernardin.ca/recipes/en/rhubarb-jam.htm?Lang=EN-US I don't care for this recipe, as I find it way too sweet (it has twice the sugar and no lemon), but it is the "correct" way to make it.