To start with, chop the anchovy fillets as small as possible and crush them to a paste in a mortar (if you haven't got a mortar, a small bowl and the end of a rolling pin will do).Put the capers in a small sieve and rinse them under cold, running water to remove the vinegar they were preserved in. Dry them on kitchen paper and chop them as minutely as you can and add them to the anchovies. Next add the mustard, garlic, lemon juice and some freshly milled black paper and mix well. Now add the oil, mix again and check the taste to see how much salt to add. Just before serving, sprinkle in the chopped herbs and again mix thoroughly so that all the ingredients are properly combined.