Tip : If the sauce seems a little thin, make a slurry with 1 teaspoon of corn starch and 2 tablespoons of water and add to the simmering sauce a little at a time until you reach the desired consistency. The sauce should not be thick nor should it be thin.
Combine port wine, Sauce Espagnole, demi-glace and black currant jam in a medium sauce pan and bring to a boil. Reduce heat to medium low and simmer until the sauce has been reduced by half, about 30 minutes.