Ensure that the canning jars and lids are sterilized by placing them in boiling water for 10 minutes. Remove and let them cool.

Wash the cranberries under cold running water, removing any stems and spoiled berries.

In a large saucepan, combine the rinsed cranberries, sugar, water, lemon juice, and cinnamon (if using).

Heat the mixture over medium heat, stirring constantly until the sugar is dissolved. Once it begins to boil, reduce the heat to low and let it simmer.

Allow the mixture to simmer for about 30 minutes, stirring occasionally to prevent burning until it thickens.

To check if the jam is ready, place a spoonful on a plate and let it cool. Run your finger through it; if it holds its shape, it is ready for canning.

Using a ladle and canning funnel, fill each sterilized jar with the hot cranberry jam, leaving about ½ inch of headspace. Wipe the rims of the jars to remove any residue.

Place the sterilized lids on the jars and screw on the metal bands until they are fingertip-tight.

If you want to preserve the jam, process the jars in a boiling water bath for 10 minutes, ensuring that the water covers the jars by at least an inch.

Allow the jars to cool at room temperature. Check the seals after 12 hours; the lids should be concave. Store the sealed jars in a cool, dark place.

For a smoother jam, use an immersion blender to puree the mixture before filling the jars.