As the 1887 edition of the Professor's book says, "The name of this drink is a misnomer, as coffee and bitters are not to be found among its ingredients...
I didn't want to open a new bottle of port before leaving for vacation so substituted byrrh that I was trying to finish up. It was good but more subdued than the original.
I got the colour which @Gregory Moreton obtained. But Jerry Thomas says that it should look like coffee if made correctly. But I don't think I did it incorrectly. Hmm. Tasted decent, if a bit fruitier than I would expect. I did use a French Grape Brandy, not a Cognac.
Excelent drink. I followed the recipie with the addition of 2 drops of saline and the resulting cocktail is delicious.. The colour is not as per the picture the port giving a loveley purple tinge to it. subline none the less