Put the cranberries into a 5- to 8-quart slow cooker.
Scoop out about 3/4 cup of the berries and finely chop. Set aside.
Stir the sugar, Somerset Ridge Tawny or Ruby Port and half the orange zest into the slow cooker.
Season with a generous pinch of salt.
Cover and cook on high for 1 hour and 30 minutes.
Stir the cranberry sauce well and set the lid back on the slow cooker so there is a 1- to 2-inch gap, to allow for evaporation.
Cook on high for another 1 1/2 to 2 hours, stirring at least twice, taking care around the edges, until many of the berries have popped and the sauce has thickened and is syrupy.
Stir in the reserved chopped cranberries and the remaining orange zest.
Spoon the cranberry sauce into a serving bowl, cover, and chill in the refrigerator until ready to serve.
