Start by rinsing your cranberries under cool water in a colander. Pick through them to remove any stems or berries that look bruised or overly soft. Once cleaned, pat them dry and place them directly into the basin of your slow cooker.
Add the sugar, orange juice, orange zest, ground cinnamon, and salt to the cranberries. Stir everything together until the berries are well coated in the sugar and liquid. Do not add the alcohol-free vanilla yet, as adding it at the end preserves its delicate flavor.
Cover the slow cooker with its lid. Set the temperature to High and cook for about 90 minutes to 2 hours, or set it to Low for 3 to 4 hours. You will know it is ready when the cranberries have burst and the liquid has turned into a deep, glossy red syrup.
Once the cooking time is up, stir in the alcohol-free vanilla. Use the back of a large spoon 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, more rustic texture.
Turn off the slow cooker and remove the lid. Let the sauce cool in the ceramic pot for at least 30 minutes. The sauce will naturally thicken significantly as it reaches room temperature. Transfer it to a serving bowl or an airtight container for chilling.
