Heat the butter and oil in a frying pan and brown the chicken evenly. Transfer to a plate using a slotted spoon and keep warm in oven.

Add the onion to the cooking juices in the pan and cook until softened but not colored. Stir in the wine, then boil for 2-3 minutes. Add the stock and bring to the boil.

Return the chicken to the pan, cover with tight-fitting lid and cook very gently for about 30minutes, until the chicken juices run clear when pierced with the point of a knife. Then transfer the chicken to a warm dish, cover and keep warm.

Boil the cooking juices hard until they are reduced to about 60ml/4 tbsp. Remove the leaves from the herbs and add to the pan with the watercress leaves and cream. Simmer over a moderate heat until slightly thickened.

Return the chicken to the casserole, season to taste with salt and pepper and heat through for a few minutes. Garnish with watercress leaves to serve.