Put the wine, vegetables, herb sprigs, bay leaves, bacon, peppercorns and stock powder or cubes in a large pan. Bring to the boil, then simmer for 10 mins.
Remove any excess fat from the chicken and push it into the liquor.
Return the liquor to the boil, then turn heat down. Cover and cook for 11⁄4 hrs until chicken legs feel tender when pierced. Remove from heat, stand for 15 mins, then lift onto a plate. Strain the liquor into a bowl and pour 500ml into a pan. Boil to reduce by half.
Pull and cut the bird into neat portions, discarding skin, wing tips and backbone. Put on a plate and cover.
Beat together the yolks, cream and tarragon in a jug. Ladle in a quarter of the liquor, mix, then pour back into the stock and turn the heat down. Mix the cornflour with a little water and add. With a wooden spoon, stir for 3-5 mins until it begins to thicken.6 Remove from the heat, then stir in lemon juice to taste. Pour some sauce over the chicken and put the rest in a jug. Serve with boiled long grain rice.