Remove the giblets, then wash and dry the chicken. Tuck the wings back and underneath the backbone until they stay in place. Season liberally with kosher salt or sea salt and lots of black pepper.
Preheat the oven to 275 degrees F.
Heat a large Dutch oven over medium to medium-high heat.
Add 1 tablespoon extra-virgin olive oil to the hot pot and brown the chicken breast-side down first, turn using a wooden spoon or closed tongs placed in cavity.
Once the bird has browned on both sides, remove the chicken to a plate and add the onion, celery, carrot, garlic, rosemary, bay leaf, salt, and pepper, and cover the pan. Sweat the vegetables to make a little pan juice, 5 to 6 minutes, stirring occasionally. Place the bird atop the vegetables and cover the pot. Transfer to the oven with the rack at the oven bottom, and roast about 1 1/2 hours, until a thermometer reads a minimum of 165 degrees F at the thickest part of the bird.
About 15 to 20 minutes before the chicken comes out of the oven, place the potatoes and turnips in a pot, cover with water, bring to a boil, and cook to tender. Drain, and mash with milk, and ripe camembert cheese. Season the potatoes with salt, pepper, and nutmeg, to taste. Cover and turn off the heat to keep potatoes warm.
Place the chicken on a carving board and cover with foil.
In a large pot, bring a few inches of water to a boil for the green beans. Salt the water, and boil the beans 5 to 6 minutes for tender-crisp. Drain and dress with butter.
Pour the pan juices and scrape the solids through a strainer into a bowl and return the pan to stovetop over medium heat. Press down on straining solids to collect all of the pan juices. Add the wine to the hot pan, and scrape up the drippings. Pour in the juices and reduce over a rapid simmer for about 10 minutes to concentrate the flavors. Add the lemon juice and turn off the heat. Transfer to a gravy boat or serving dish.
Carve the chicken and serve with pan juices, potatoes, and beans.
Leftover chicken makes for a delicious addition to any salad, or serve as sandwiches with sliced pears, lemon-dressed watercress, Cheddar cheese, and chutney.