Place the chicken pieces in a large saucepan, cover with water, add the onion, carrot and a pinch of salt and bring to the boil. Lower the heat and simmer for 45 minutes or until chicken is tender.
Transfer the chicken pieces to a plate and, when cool enough tohandle, discard the skin and strip the flesh from the bones. Return the bones to the stock and simmer unti the stock is reduced.
Cut the chicken into strips.
Grind the walnuts and bread in a blender and turn into a saucepan.
Remove bones from stock. (cooks note: at this point, I use an immersion blender and smooth out the the carrots & onions) Stir in stock into bread & walnut mixture until you have a smooth paste. Season with the salt & pepper. If the sauce is too thin, simmer over a low heat until it thickins. Refrigerate chicken and sauce.
Put paprika and oil in bowl
Pile chicken into a serving dish. Mix in the sauce and make sure it coats and covers the chicken.
Dribble the oil and paprika over the top. Strew the chopped tarragon leaves on at the end.