Wash the apples well, and cut them into large chunks, discarding the core and seeds. Add to the crock pot.

Rinse the cranberries and add them to the crock pot. Give the fruit a stir and then cover and cook on HIGH for 4 hours. Give the pot a stir every once in a while to prevent sticking. If the mixture is sticking you can add a bit of water, but I didn't have to, the natural juices of the fruit should be sufficient.

Puree the softened fruit in a high speed blender or food processor, working in 2 batches.

Push the puree through a mesh strainer with the back of a large spoon, Force the puree through, you should be left with just a light layer of solids. Rinse out the strainer between batches.

Rinse out the crock pot and return the strained puree to the pot. Bury a stick of cinnamon into the puree. Cook on HIGH, uncovered, for another 2 hours, or until thick and spreadable, stirring occasionally to prevent sticking. When the fruit has thickened, spoon it into clean glass jars. Let cool, and then cap and refrigerate. The butter will keep for 4 weeks in the refrigerator, or up to a year in the freezer. (If you plan to freeze, leave a little space at the top of each jar to allow for expansion.)