To prepare the poussin, take off the legs, cut off the carcass to leave the breast on the crown. Scrape away the wishbone and trim away the wing bone.
Take the thigh bones out of the legs and trim off the knuckle of the drumstick (you can leave the bone in, but it won t leave you much room for the stuffing).
Leave in the fridge until ready to fill with the mushroom farce.
For the mushroom farce, finely chop the mushrooms, shallots, pancetta and garlic.
Fry the pancetta until the fat starts to run out on the bacon. Add the butter, garlic and shallots, cook for a few minutes and then add the mushrooms and thyme.
Cook the mushrooms until they are soft, add the breadcrumbs and season.
When cool fill the chicken legs. Note: The consistency should be pliable and not too crumbly and dry.
Re-shape the legs then wrap in pancetta and secure with cocktail sticks.
For the herb butter, blend all the ingredients together in a blender until you have a brilliant green colour.
Lift the breast skin off the poussin and fill with the butter. Pull the skin down, season and wrap in tin foil.
Roast the legs and breast in a moderate oven (200C/400F/Gas 6) for 20 minutes, or until cooked through. (The chicken is cooked through when the juices run clear when pierced in the thickest part with a skewer.) Remove from the oven and set aside to rest.
For the rösti, peel and grate the potatoes, squeeze out any excess water, then add the bacon, thyme and cornflour. Season with salt and pepper.
In a small frying pan heat up a little oil and add the potato mix. Fry on both sides to give colour.
For the vegetable garnish, make the emulsion by adding butter to a pan with water, heat up until the butter has melted, put to one side.
Scrub clean all the vegetables, blanch and re-fresh in iced water.
Top and tail the beans, blanch and re-fresh in iced water.
Any green vegetables should be put into boiling water and then cooked. Other vegetables can be put into cold water and then brought to the boil.
To serve, warm the chicken in the oven, eat up the vegetables in a little melted butter and warm through the rosti. Arrange neatly on the plate and garnish with watercress.
