Melt the butter on a low heat and completely clarify it by separating the fat with a ladle leaving the milky residue in the pan, keep in a warm place. Put egg yolks with vinegar, salt and a splash of cold water in a stainless steel bowl and whisk for a few minutes then place the bowl over a pan of simmering water, whisk continuously until the mixture is pale and thick this will take about 10 minutes. Remove from the pan of simmering water and slowly whisk in the melted butter, squeeze in the lemon and season with cayenne, taste if more salt is needed.
Bring a pan of water to the boil add 50ml white wine vinegar and poach eggs until soft, 3-4 minutes. Split the muffins and toast them on both sides, put a slice of ham on each and warm under the grill. When eggs are done, drain and place one on each muffin pour over a spoonful of hollandaise on each.