Classic Orange Reduction Sauce

This wonderfully delicious sauce has great character with a hint of orange once it is ready to serve.  The added orange slices may be omitted for a less orange-flavored sauce.  It is wonderful with pork or duck or spooned over fluffy white rice.

Combine sugar and water and boil over medium-high heat stirring frequently until the mixture turns into a dark syrup, about 10 minutes.  Remove from heat and add the vinegar.  When the bubbling subsides add the orange juice and shallots.  Boil fairly vigorously until reduced to about ½ cup, about 15 minutes.  Add the broth and continue to boil until all is reduced to about ¾ cup - this should take approximately 30 minutes.

At this point the sauce can be refrigerated and held for a day.  When ready to use, reheat, adding the butter, zest and Mandarin oranges.