Peel, core, and finely chop or grate the apples. Weigh them after preparation so you have 1 kg of prepared fruit and the sugar ratio remains accurate.

Place the apples, sugar, lemon juice, and water in a wide, heavy-bottomed saucepan. Add the cinnamon if using, then let the mixture stand for 15 to 30 minutes if time allows.

Bring the mixture to a boil over medium heat, stirring until the sugar dissolves. Reduce the heat and simmer uncovered for 35 to 50 minutes.

Stir frequently, especially during the final part of cooking, to prevent the jam from catching on the bottom. Mash with a potato masher for a rustic texture or blend carefully with an immersion blender for a smoother jam.

Test the jam by placing a small spoonful on a chilled plate. Let it cool briefly, then push it with a fingertip; it should wrinkle slightly and should not run freely.

Remove the saucepan from the heat and stir in the vanilla if using. Spoon the hot jam into clean, sterilized jars, leaving a little headspace.

Cool the jars, cover them, and refrigerate the jam. Use a tested water-bath canning recipe and current processing guidance if you want room-temperature storage.