Begin by removing the crust from the bread.
Place the crustless bread on a plate or in a bowl and cover with the vinegar.
Squeeze the bread, then place it in a blender with the parsley, egg yolk, anchovy, capers, garlic and salt.
Slowly add the olive oil as you blend.
Continue blending until you have a green, fairly uniform mixture.
If you want, you can increase the amount of herbs in the sauce.