In a large stainless steel bowl, mix the sliced rhubarb with the sugar until all pieces are well-coated.

Let the mixture sit at room temperature for about 2 hours so the rhubarb releases its juice.

While waiting, boil water for the canner and prepare your jars, lids, and rings.

Once the rhubarb has released enough juice, strain the fruit from the liquid and set the slices aside.

Measure out 3 cups of the juice. If you don't have enough, add a bit of water to make up the difference.

In a large pot, whisk together the rhubarb juice, lemon juice, and Clearjel. Bring this to a boil over medium-high heat, stirring often.

Once boiling, the mixture should thicken after about a minute. Add the rhubarb slices and stir to coat them well. Bring it back to a boil, stirring frequently to prevent sticking.

Remove the pot from the heat.

If freezing, ladle the filling into freezer-safe containers, leaving 1 inch of headspace. Seal and let cool to room temperature before freezing.

If canning, ladle the filling into prepared jars, leaving 1 inch of headspace. Remove air bubbles, wipe the jar rims clean, and place the lids and rings.

Process quart jars for 20 minutes (15 minutes for pints), adjusting the processing time for your elevation.

After processing, remove jars from the canner and let them cool. Check the seals, remove the rings, and store the jars. Refrigerate or freeze any jars that didn't seal properly.