Begin by rinsing your fresh cranberries under cold water and picking out any soft or bruised berries. Place the cleaned cranberries directly into the basin of your slow cooker. If you are using frozen berries, there is no need to thaw them first, you can put them in exactly as they are.
Add the granulated sugar, orange juice, water, salt, and orange zest to the slow cooker. Stir the mixture gently to ensure the sugar is evenly distributed among the berries. Finally, tuck the cinnamon stick into the center of the mixture to ensure the flavor infuses thoroughly during the cooking process.
Cover the slow cooker with its lid and set the temperature to high. Cook the mixture for 3 to 4 hours, or if you have more time, you can set it to low for 7 to 8 hours. You will know it is ready when most of the cranberries have burst and the liquid has turned into a thick, bubbling syrup.
Once the cooking time is up, remove the lid and discard the cinnamon stick. Stir in the alcohol-free vanilla extract. If you prefer a smoother sauce, you can use a potato masher or the back of a large spoon to crush some of the remaining whole berries. Transfer the sauce to a bowl and let it cool completely, as the sauce will continue to thicken significantly as it reaches room temperature.
