Clean, wash and coarsely dice the greens. Peel and quarter the onions.
Tie the bay leaves, thyme, tarragon and parsley into a bouquet of herbs. Slice the lemons.
Bring 2 tablespoons of salt to a boil with 4 quarts of water and add the spices, onions, greens and lemon slices. Gut the poulards, rinse them, add them to the broth with the bones and simmer over medium heat for 1 ¼ hours, do not boil. Then remove the poularden from the broth with a skimmer and set aside. Pour the broth through a fine sieve.
Reduce 1 quart of the broth to ¼ quart.
Whisk the egg yolks. Finely chop the tarragon and stir into the reduced broth with the lemon juice and crème fraîche. Then chill. Skin the poulards and break them apart. Arrange the breast halves and thighs on a platter and cover with the creamy tarragon sauce.