Clean the vegetables (leave some green for carrots and fennel) and wash them. Cut the fennel into slices and sprinkle with lemon juice. Cook vegetables in boiling salted water for about 12 minutes.
Orange hot rinse, dry. From half of the orange peel in narrow strips, rub off the rest. Squeeze the juice. Whip 4 tablespoons of juice, grated peel, egg yolk, wine and pepper in a hot water bath until creamy.
Beat butter (up to 2 tablespoons) first drop by drop, then in a thin stream. Season sauce with salt and pepper. Drain the vegetables. Swivel in the remaining hot butter. Arrange ham, vegetables and sauce on a plate.
Garnish with chervil. Remaining sauce extra is enough. Garnish with orange peel strips and chervil leaves.