Prepare Cherries: Remove the stems from the cherries and give them a good rinse. Use a stiff straw to push through each cherry to remove the pit. Chop cherries into large pieces or place them in a blender and blend until desired consistency. Measure out 8 cups of fruit.
Prepare Apple: Place the skins and core of an apple onto a piece of cheesecloth and tie it into a bundle.
Cook: Place the cherries, apple bundle, sugar and lemon juice into a heavy saucepan. Boil the mixture, stirring constantly, until thickened. About 20-25 minutes.
Check for Doneness: While the jam is cooking, place a small glass plate in the freezer. When you are ready to check the jam for doneness, spoon a small amount onto the plate and put it back into the freezer for 2 minutes. Run your finger through the jam. If it stays separated it's ready. If it runs back together, it needs more cooking time.
How to store: Pour the jam into a container and store in the fridge for up to 4 weeks or follow the canning instructions to store in your pantry for up to 18 months.