For the sauce
Put the lemon in the cavity of the chicken, then put the chicken in a saucepan that it just fits. Add the onion, carrot, peppercorns and salt to the pan.
Add sufficient water to come two-thirds of the way up the chicken, bring to the boil, then cover and cook gently for about 1 1⁄2 hours until the chicken juices run clear.
Transfer the chicken to a large bowl, pour the cooking liquid over it and leave to cool. When cold, strip the meat from the chicken, discarding the skin and bones, then chop or tear the meat into bite-size pieces.
To make the sauce, take a frying pan and sweat the onion in the butter until soft. Add the curry paste, tomato purée, wine, bay leaf and lemon juice, then cook for 10 minutes. Add the jam, then push the mixture through a sieve and leave to cool.
Beat the mixture into the mayonnaise. Fold in the cream, then season with salt and pepper. Stir in the chicken pieces until evenly coated. Chill until ready to serve, garnished with a little watercress.