How to Make It
Preheat the oven to 450°. In a medium roasting pan, spread the onion and carrot slices in an even layer. Set a rack in the pan. Season the cavity of the chicken with salt and pepper and stuff it with the thyme and rosemary sprigs and 1 teaspoon of the lavender. Tie the legs together with cotton string. Rub the 1 tablespoon of softened butter all over the chicken and season with salt and pepper. Set the chicken on the rack, breast side up. Sprinkle the chopped thyme and rosemary and the remaining 1 teaspoon of lavender buds over the chicken. Roast the chicken for 15 minutes.
In a glass measuring cup, combine the stock and wine. Baste the chicken with 2 tablespoons of the stock and wine mixture. Turn the chicken on its side and roast for 10 minutes. Baste again, turn the chicken on the other side and roast for another 10 minutes. Reduce the oven temperature to 350° and baste, then roast the chicken for 15 minutes longer. Turn the chicken breast side down, baste and roast for 15 minutes. Turn the chicken breast side up and baste. Roast the chicken for about 25 minutes longer, basting once. The chicken is done when the juices run clear and an instant-read thermometer inserted in the inner thigh registers 165°.
Transfer the chicken to a carving board and let rest in a warm place for 10 minutes. Remove the rack from the roasting pan. Set the pan over 2 burners on moderate heat. Pour the remaining 1/4 cup of basting mixture into the pan and simmer for 2 minutes, scraping up the browned bits from the bottom of the pan. Strain the pan juices into a small saucepan, pressing on the solids. Skim off the fat and bring the jus to a simmer. Remove the saucepan from the heat and whisk in the 1 tablespoon of chilled butter until blended. Season with salt and pepper. Carve the chicken and serve with the herb jus.