Sauté onions about 8 minutes until translucent. Add garlic, rosemary and thyme and cook 1 minute further.
Add broth and orange juice and boil until liquid is reduced to about ¾ of a cup. This may take 5-8 minutes.
Strain sauce into a saucepan. (Reserve solids - if you are making stuffing you can add them to the dressing. See Recipe Note below.)
Add cranberries and sugar and boil until berries pop - about 5 minutes.
Mix port and cornstarch in a jar and shake well to blend. Add mixture to the sauce and boil a few minutes until sauce thickens. Add salt and pepper and stir well. (Sauce can be made a day ahead of time.)
Serve warm.
Notes
Recipe Note 1: I served this Port Cranberry Sauce with Stuffed Pork Loin Roast. If you are making a stuffing as part of your meal you can save the solids from the cranberry sauce to add onion and spice to your dressing.