Pit and roughly chop the Damson plums.

Combine the plums, blueberry juice, vanilla extract (or vanilla bean), vodka (or lemon juice or red wine vinegar), cinnamon stick, star anise, and cloves (if using) in a medium heavy-bottomed pot.

Bring the mixture to a boil over medium-low heat, then reduce the heat to very low and simmer for 1 hour, stirring every 15 minutes to prevent sticking, until the plums have broken down and the liquid has reduced.

Dissolve the kuzu in 2 teaspoons of water to make a slurry.

Add the kuzu slurry to the simmering plums and mix thoroughly.

Bring the plum mixture to a low boil and let it continue for about 5 minutes.

Reduce the heat and simmer for another 20-30 minutes, until the liquid is thickened and reduced to the desired consistency.

Remove the pot from the heat and let it cool for 10-15 minutes.

Remove the cinnamon stick and/or star anise, if used.

Pour the cooked plums into a blender and blend until smooth.

Pour the smooth plum preserves into a sterilized jar (or several small jars).

Seal the jar(s) and refrigerate.

Serve the preserves on toast, grain-free almond muffins, or dollop onto yogurt.