For this recipe, it’s important to use a big, fruity-tasting olive oil, because it will be the foundation flavor here. You want one with a round fragrance and as little bitterness as possible.
Put the egg in a small saucepan, and cover with cold water. Place the pan over medium-high heat, and bring to a boil. As soon as it boils, remove the pan from the heat, cover it, and set a timer for 12 minutes. When the timer goes off, drain away the hot water and rinse the egg under cold water until it is thoroughly cool.
Meanwhile, combine the shallot and the lemon juice in a small bowl. Set aside to macerate while you prepare the rest of the sauce.
Combine the parsley, chervil, chives, lemon zest, capers, cornichons, and olive oil in a small bowl. Whisk well. Peel the egg, and then finely chop the yolk and dice the white. Add the egg to the bowl. Add the lemon juice, shallots, and a good pinch of salt, and whisk well. Taste, and adjust with more lemon juice and salt, if needed.
Serve over asparagus, steamed or boiled potatoes, grilled endives, fish, cold roasted chicken, or other cold leftover meats.