My father was a Shanghai Marine in the thirties then a POW and returned after the war and made a recipe similar to this every year. The difference was more whiskey (two fifths for quart of milk and quart of heavy cream) and two lbs sugar. Later this just became 2 quarts 1/2 and 1/2. Dark rum same. But major difference is that he never used bourbon whiskey - only straight rye. Back then it was Old Mr. Boston. Now I use either Old Overholt or Jim Beam. The rye produces a very smooth egg nog. Whip the egg whites to soft peaks and fold them in at the start. Shake bottle before pouring. Never have heard anyone mention an origin of this from Shanghai so that is pretty cool.