Prep your fruit. Chop apples into small chunks and rinse cranberries if you’re using fresh ones. No need to audition your knife skills—just small bites that cook evenly.
Combine everything in a heavy-bottomed pot. The apples and cranberries will start to break down as the liquid swirls in. Stir well to get all the sugar mixed in.
Bring to a gentle boil over medium heat, then reduce to a simmer. Simmer 25–35 minutes, stirring occasionally, until the mixture thickens and looks jammy. If it’s too runny, cook a few minutes longer; if it’s too tight, splash in a touch more juice.
Skim off any foam that forms on top. It’s not glamorous, but it keeps the jam clear and glossy.
Test the set. Put a small plate in the freezer while it cooks, then drop a spoonful on the plate. If it wrinkles when you push it, you’re done. If not, cook a bit longer and test again.
Remove from heat and let it cool a bit. Ladle into clean jars, seal, and refrigerate. Or can it for longer storage if you’re feeling ambitious.