Step 1The night before, wash and thoroughly dry the chicken. Lightly salt the cavity and the outside of the chicken with kosher salt (kosher salt is essential). Loosely drape the chicken in paper towels, place in a pan or on a tray in the refrigerator and leave overnight.
Step 2Remove the chicken from the refrigerator 3 hours before you want to roast it. Rinse off the salt, dry the chicken and carefully place three thin slices of truffle (about one-sixth-inch thick) under the skin on each of the side of breast (six slices total), being careful not to rip the skin. Tie the chicken legs together with kitchen twine and let the chicken rest for 3 hours.
Step 3Heat the oven to 450 degrees. Heat a small heavy roasting pan (preferably not much larger than the chicken) at 450 degrees for 10 minutes.
Step 4Place the chicken in the hot roasting pan (no rack), breast side up. You'll hear a sizzle and know it's hot enough. A 4-pound chicken should take 55 minutes to 1 hour to roast. No basting is needed.
Step 5When the chicken is done, set aside on a cutting board, cover loosely with aluminum foil to keep it warm.
Step 6Meanwhile, pour off everything but a tablespoon or so of fat and set the roasting pan over a burner, scraping up the caramelized bits with a wooden spatula, and adding a splash or ladle of chicken stock, probably about a cup. Cook until it's reduced and slightly thickened, remove from the heat, and whisk in 2 tablespoons of room temperature truffle butter.
Step 7Pour the juices into a sauce boat and add a tablespoon of minced truffle. Serve on the side with the chicken carved into pieces.