Fill medium sized pot with water and place on stove to boil. Add vinegar to water.
Mix 1 egg, buttermilk, cornstarch and cayenne pepper in medium saucepan. Cook on low until thickened, mixing frequently with whisk. Turn off heat and add butter & lemon juice. Mix with whisk, cover and keep warm.
Add one egg to a small cup and gently add to the slightly boiling water. Repeat and add one more egg. Cook 3-5 minutes and gently remove with a slotted spoon. Remove to paper towels. Cook the other two eggs repeating the same procedure.
Toast English muffins, add the ham, top with poached eggs, spoon on the buttermilk mixture and a sprinkle of dried parsley.