Place turkey and enough brine to cover in a large pot. Refrigerate for 12-24 hours. If turkey floats to top weigh down with a plate and cans to keep it submerged in brine. Preheat oven to 400 degrees rub 2 tablespoons mushroom and sage olive oil over the skin of the turkey. Sprinkle pepper over skin and in cavity. Tuck wing tips under loosely truss legs and place turkey on a V shaped rack in roasting pan. Tent breast with foil. Put turkey in preheated oven. To ensure the bird cooks evenly rotate roasting pan 180 degrees every 30 minutes. Roast for about one hour remove foil and baste turkey with 1/2 cup of warm stock mixed with one tablespoon mushroom and sage olive oil. Start checking internal temperature after about one hour by inserting an instant read thermometer in the meatiest part of the thigh not touching the bone. If legs or breast begin to get too brown cover loosely with foil roast until internal thigh temperature reaches 165 degrees. Total roasting time should be about 2-2 3/4 hours. Let bird rest at least 20-30 minutes before carving.