Rinse the cranberries under cold water and remove any stems or bruised berries. Place them in the slow cooker.
In a separate bowl, mix the orange juice, sugar (or maple syrup), ground cinnamon, ginger, cloves, nutmeg, and orange zest until well combined.
Pour the mixture over the cranberries in the slow cooker. Stir gently to combine.
Add a pinch of salt to enhance the flavors and mix again.
Cover the slow cooker and set it on low for 4-6 hours or high for 2-3 hours until the cranberries have burst and the sauce has thickened. Stir occasionally if possible.
If using, add the chopped pecans or walnuts in the last 30 minutes of cooking for added texture.
Once done, taste and adjust the sweetness, adding more sugar or maple syrup if needed.
Allow the sauce to cool slightly before transferring it to a serving dish or container. It will thicken further as it cools.
Notes
Serve in a decorative bowl and garnish with rosemary or orange slices.