Makes 50 hors d’oeuvres.
25 white icicle radishes, peeled and halved lengthwise
Make the tapenade:
In a small bowl let the anchovy fillets soak in 2 tablespoons of the milk for 10 minutes, drain them, and pat them dry. In another small bowl let the bread soak in the remaining 6 tablespoons milk for 10 minutes and squeeze out the excess milk. In a food processor fitted with the steel blade or in a blender purée the olives, the anchovies, the bread, the hard-boiled egg yolks, the capers, the lemon juice, the garlic and the mustard, with the motor running add the oil in a stream, and blend the mixture until it is smooth. Transfer the mixture to a small bowl and chill it, covered, for at least 2 hours or up to 1 week.
Scoop out a trough from the cut side of each radish half with a 1/2-inch melon-ball cutter, dropping the radishes as they are cut into a bowl or ice water, transfer the radishes cut side down to paper towels, and let them drain for 5 minutes. Invert the radishes, transfer the tapenade to a pastry bag fitted with a small star tip, and pipe it into the radishes. (The radish boats may be prepared up to 2 hours ahead and kept chilled, covered loosely.) Arrange the hors d’oeuvres decoratively on a platter.