Peel and core the apples, then chop them into small cubes, about 1/2-inch in size. Trim the rhubarb stalks and cut them into similar-sized pieces.

In a heavy-bottomed pot, mix the chopped apples and rhubarb with sugar, lemon juice, and cinnamon until well combined.

Place the pot on medium heat, stirring occasionally to dissolve the sugar completely until small bubbles form at the edges, about 5-7 minutes.

Reduce heat to low and let the jam simmer for 20-30 minutes, stirring frequently until thickened.

Remove from heat and mash the fruit to your desired texture using a potato masher or fork.

Allow the jam to cool slightly before transferring to sterilized jars and sealing tightly.