Wash and dry the parsley thoroughly and then chop finely.
Remove the crusts from the stale bread and slice into small pieces. Place the bread in a bowl and sprinkle with the vinegar. Leave to rest for a few minutes and then squeeze the bread to remove the excess liquid.
Place the bread into a mixer bowl. Add the anchovies, the desalted capers and the garlic, taking care to remove the core. Blend the ingredients into a paste. Add the chopped parsley to the contents of the mixer bowl.
Hard boil the eggs, remove the shells and set the yolks aside. Add the egg yolks to the other ingredients by passing them through a fine sieve.
Mix all the ingredients thoroughly and add the oil gradually until the mixture assumes the consistency of a proper sauce. Taste and, only if required, add salt.
