Season the poussin with a generous sprinkling of salt and freshly ground black pepper.
Heat the olive oil together with the butter in a saute pan with straight sides (sauteuse) over medium heat. Add the poussin, without crowding, to the saute pan skin side down and cook slowly to brown the chickens to a golden brown color. Turn the chickens to brown the other side, add the pearl onions to caramelize with the chicken, and place a lid on the pan. Allow the chicken and onions to simmer together for 5 to 7 minutes.
Add the dry sherry to the saute pan and cook down to reduce the liquid until almost evaporated.
Add the hot stock together with the spices tied in cheesecloth into an herb bouquet garni.
Let this simmer slowly over low heat for 30 to 35 minutes. After 20 minutes has gone by add the morels to the pan and continue to simmer all together for the remaining 15 minutes cooking time.
Remove the chicken carefully from the pan, add the peas and asparagus to the stock and cook for 2 minutes. Stir in the creme fraiche and cook together for 2 more minutes before spooning the vegetables around the chicken and pouring the excess sauce into a sauceboat. Sprinkle chopped chives over everything and serve.