A large marble mortar is much the easiest to work with—lacking that, use a wooden bowl. Pound the capers to a paste with the seasonings, add the anchovies, pound, add the tarragon, the parsley, and the greens, pounding to a purée. Pound and stir in the soaked bread, then the egg yolks, and, when the mixture is absolutely smooth and uniform, begin dribbling in the olive oil, stirring vigorously and uniformly with the pestle as if mounting a mayonnaise. Taste for seasoning and stir in the vinegar or lemon juice to taste. If prepared ahead of time, the emulsion may not hold, traces of oil separating and appearing at the surface; give it a rapid beating with the pestle just before serving.