Into a pot, place rhubarb slices, frozen raspberry and lemon juice. Cook on low-medium heat, until super soft

Stir rhubarb occasionally, and start mashing with either potato masher, spoon, or spatula. Be extra careful that rhubarb will splatter and it can be very hot

Meanwhile, mix pectin with lemon juice and sugar

Once rhubarb is super soft and mashed, stir in pectin, continue cooking on low heat until completely combined

Add in the last sugar and stir for another 3-5 minutes

Take off from heat and ready to be canned!

If you use waterbath method, jam is good for months and months, if fridge method, jam is good for 8-10 weeks