Preheat your oven to 400 F. Cut the plums in half, remove the pits, and sit them on the tray skin side down. Don't bother adding parchment. It's not necessary and does not stop the juice from getting on the tray (Don't worry, it's not difficult to remove). Bake for about 20 minutes ensuring they don't burn.
Allow to cool slightly.
Add all of the plums, their juices, applesauce, and the sugar to a high speed blender. Blend until smooth. Taste it! Add additional sweetener if you'd like. You will probably have to blend multiple batches. I poured it all into large bowl and stirred in the lemon juice and cinnamon.
Line your silicone trays with parchment paper. Pour the pureed mix onto silicon trays ensuring mix is only about ⅛ to a ¼ inch thick. The thicker it is in the center the longer it will take to dry. Thin is the goal.
Set your dehydrator temperature at 135 F and dehydrate for about 12-14 hours. Having said that, it really depends on how thick your mixture is and how large your trays are so watch it hourly after about 8 hours to ensure it doesn't get too dry. You will know it's done because the center will no longer feel wet and the leather will have a smooth appearance.
Cut into strips with scissors and store on the counter or in the fridge in ziplock bags or containers with lids.
Recipe by WHAT the HECK do I eat NOW at http://whattheheckdoieatnow.com/2024/08/22/fresh-plum-fruit-roll-ups/