Wash the plums well, remove the stones, and slice the fruit.

Peel and grate the sour apples.

In a large saucepan, combine the sugar and cinnamon sticks with 5 cups of water.

Bring the mixture to a boil, stirring until the sugar dissolves.

Continue boiling until a syrup begins to form.

Add the sliced plums and grated apples to the saucepan.

Bring the mixture back to a boil, then reduce heat and simmer, stirring occasionally to prevent sticking.

Continue simmering until the jam thickens and bubbles form on the surface.

To test for doneness, remove a spoonful of jam and place it on a dry white plate.

Quickly cool the jam and draw the tip of a spoon across it.

If the jam leaves a clear path, it is ready.

Stir in the lemon juice and brandy (if using) and mix for two more minutes.

Remove the saucepan from the heat.

Discard the cinnamon sticks.

Carefully fill the sterilized jars with the hot jam, leaving about 1/4 inch headspace.

Seal the jars tightly.

Turn the jars upside down until completely cool to ensure a proper seal.