Prepare the Berries: Wash the fresh mulberries gently in a colander under cold running water. Pat them dry with a paper towel. Use kitchen scissors or your fingers to pinch off any tough, woody green stems from the tops of the berries.

Combine Ingredients: Place the prepared mulberries into a medium heavy-bottomed saucepan. Add the granulated sugar, fresh lemon juice, and water.

Simmer the Sauce: Place the saucepan over medium heat and bring the mixture to a gentle boil, stirring frequently to ensure the sugar dissolves completely. Once boiling, immediately reduce the heat to low so the sauce is just barely simmering.

Break Down the Fruit: Let the sauce simmer gently for 10 to 15 minutes. As it cooks, the mulberries will soften and release their deep purple juices. Use a wooden spoon or a potato masher to gently crush the berries against the side of the pot. Leave it chunky for a rustic topping, or mash it thoroughly for a smoother syrup.

Thicken and Cool: The sauce will begin to thicken slightly as the natural pectins in the fruit release. Remove the saucepan from the heat and stir in the vanilla extract if using. Keep in mind that the sauce will continue to thicken significantly as it cools.

Serve or Store: Serve the warm sauce immediately over pancakes or waffles, or let it cool completely to room temperature before transferring it to a glass mason jar for storage.