Peel, core, and dice apples. Add to a saucepan with the rhubarb. Cover with water. Bring to a boil. Reduce heat and let simmer 20 minutes or until rhubarb is soft. Drain.
Combine rhubarb mixture with honey. Add cooking liquid until desired consistency is reached (note: if you like the consistency without adding the cooking liquid, you don't have to add any.)
Instant Pot
Peel, core, and dice apples. Add to instant pot with the rhubarb. Add 1/2 cup water. Lock lid, set valve to sealing. Program for manual-high and 8 minutes. Allow for Natural Pressure Release (NPR). Stir in honey.
Notes
We used fuji apples for testing purposes. For vegan version, use pure maple syrup or agave in place of the honey.