Preheat oven to 400 F.
Wash the chicken under cold running water then pat dry. Combine the garlic and butter and spread the mixture under the skin of the chicken and all over the body. Season the bird all over including the cavity with kosher salt and freshly ground black pepper. Take half of the thyme and rosemary and put this along with the garlic and any remaining butter inside the cavity. Fold the wing tips under the bird and tie legs together with kitchen twine.
Take a large roasting dish and add the mushrooms and shallots. Scatter remaining thyme and rosemary over the pan and add the Marsala and stock (depending on the depth of your roasting pan you may not need all of the marsala and stock - it should be enough to cover the bottom of the pan but not submerge the mushrooms and shallots). Place the chicken(s) on top and drizzle some extra-virgin olive oil over the whole pan and season with salt and freshly ground black pepper.
Roast in the hot oven for 1 hour or until the internal temp of the bird registers 160 F between the leg and thigh. You may need to add more stock to the bottom of the pan if all the liquid evaporates while cooking. When done, place the bird on a plate and rest for 20 minutes. Meanwhile take the pan with the mushrooms, shallots and juices and gently simmer over low heat on the stove-top whilst scraping the bottom of the pan to loosen all the browned bits and extract all the flavor. Skim any excess fat off the jus and discard. Give it a final taste and seasoning before serving the roasted marsala mushrooms and shallots with the herb roasted chicken and jus.