Prepare the chicken the day before. Use the pointed end of a knife to pierce the chicken in several places. Then insert the anchovy, garlic clove and rosemary sprig in each opening. Cover with plastic wrap and place in refrigerator over night.
The next day, combine the tarragon leaves, shallot and crème fraiche in a bowl and mix through well. Remove the chicken from the refrigerator and stuff the chicken with the tarragon mixture.
Preheat the oven to 180C (350 °F/Gas 4).
Take a chicken, a good knife and some kitchen string. Remove the innards of the chicken and set it down so the breast is facing you.
Tie the string around the neck skin and the wings, then tuck these underneath the chicken.
Pass the string over the breast, slip it under the thighs and wrap it around the end of the drumsticks. Take the string back to the upper wings.
Wrap the string around the wings several times, pull the string tight, then tie a knot.
Then put it in a flameproof roasting tin. Drizzle the olive oil over the chicken, then roast for 1 hour and 30 minutes in the oven.
Carve the chicken into portions and serve with the stuffing