Set up a double boiler by putting a pot of water on to simmer and using a heat-proof bowl either strong glass or metal that fits on top of the pot but does not touch the water. The steam will heat the bowl which will heat the ingredients
Mix vinegar, oil, Dijon, shallots in a separate bowl
Whisk the egg yolks in the bowl over the steaming pot for 1 minute
While still whisking gradually drizzle the other ingredients
Keep gently whisking the hollandaise, it will slowly thicken from the heat
Sauce is ready when is coats the back of a wooden spoon or reaches 65 degrees Celsius. Can be kept at that temperature while you assemble the other ingredients.
Toast and butter muffins. Poach eggs. Assemble eggs and ham on muffins and pour over the hollandaise sauce. Garnish with parsley