Preheat the oven to 200C. Wash and dry the poussins. Spread the softened butter all over the poussins and put a hazelnut-sized piece in the cavity of each bird.

Mix together the shallots and parsley and place a quarter of the mixture inside each poussins. Put the poussins side by side in a large roasting tin and roast for 40-50 minutes, or until the juices run clear when the thickest part of the flesh is pierced with a skewer.

Transfer the poussins to a warmed serving plate. Cover and keep warm.

Skim off most of the fat from the roasting tin, then add the grapes and vermouth. Place the tin directly over a low heat for a few minutes to warm and slightly soften the grapes.

Lift the grapes out of the tin using a slotted spoon and scatter them around the poussin. Keep covered.

Stir the corn flour into the cream, then add to the tin juices. Cook gently for a few minutes, stirring, until the sauce has thickened. Season to taste with salt and pepper.

Pour the sauce around the poussins. Sprinkle with the toasted pine nuts and garnish with watercress sprigs.