In a medium frypan, fry the bacon on each side until evenly browned.
Fill a large saucepan with about 8cm water, and bring to a simmer. Pour in the vinegar.
Carefully break the 4 eggs into the water, and cook 2 to 3 minutes, until whites are set but yolks are still soft. Remove eggs with a slotted spoon.
Meanwhile, melt the butter until bubbly in a small pan or in the microwave. Remove from heat before butter browns.
In a blender or food processor, blend the egg yolks, cream, cayenne pepper and salt until smooth. Add half of the hot butter in a thin steady stream, slow enough so that it blends in at least as fast as you are pouring it in.
Blend in the lemon juice using the same method, then the remaining butter.
Place open English muffins (or toast) onto serving plates. Top with 1 slice bacon and 1 poached egg. Drizzle with the sauce, and serve at once.