Position a rack in the lower third of an oven. Preheat to 450°F. 2 Rinse the chicken and pat dry with paper towels. Smear 1 tbsp of the butter and the 1/2 teaspoon salt inside the chicken. Rub the outside of the chicken with the remaining 1 tbsp butter and salt and pepper to taste.

Strew the onion, celery, and carrot in the bottom of a flameproof roasting pan. Top with the chicken breast, skin side up. Scatter the shallots around the chicken.

Roast the chicken and shallots for 20 minutes.

Meanwhile, combine 1 cup of the Chardonnay, the lemon juice, half of the minced chervil, and a touch more salt and pepper. After 20 minutes, pour the wine mixture over the chicken, reduce the temperature to 350°F, and continue roasting, basting occasionally with the pan juices, until the juices between the thigh and the body cavity run clear, about 1-1/4 hours longer.

Remove the chicken to a cutting board that has a trough to catch the juices. Lift out the shallots with tongs and reserve.

Pour the juices of the roasting pan through a sieve placed over a 2-cup measuring cup, leaving the glazed brown bits on the pan's bottom. Discard the vegetables. Set the measuring cup in the freezer briefly to force the fat to rise. Skim off and discard the fat. If there are less than 2 cups juices, add water as needed to achieve measure.

Place the roasting pan on the stove top over medium-high heat. Sprinkle with the flour and whisk well, dislodging the browned bits and cooking the resulting paste for 1 minute. Slowly add the remaining 1/4 cup wine, then the pan juices. Bring to a boil and boil until the sauce is as thick as you like. Remove from the heat and add the remaining minced chervil. Pour into a warmed sauce boat.

Garnish the chicken with the reserved shallots and the chervil sprigs and carve at the table. Pass the sauce at the table.