Place the cranberries, sugar, orange juice, orange zest, and salt into the basin of your slow cooker. Stir the mixture well to ensure the cranberries are evenly coated with the sugar and liquid. Nestle the cinnamon stick right into the center of the berries to ensure the spice infuses throughout the cooking process.
Cover the slow cooker with its lid and set the temperature to high. Let the sauce cook for about 3 hours. You will know it is getting close when you start to hear the cranberries making a soft popping sound as they burst from the heat. The liquid will begin to turn a deep, vibrant red and the sugar will be completely dissolved.
Once the cook time is up, remove the lid and carefully take out the cinnamon stick. Use a fork or a potato masher to lightly crush some of the cranberries if you prefer a smoother sauce, or leave them as they are for a chunkier texture. Stir in the alcohol-free vanilla extract and let the sauce sit uncovered for about 20 minutes to thicken as it cools.
