Step 1Wipe the turkey inside and out with a damp paper towel. Place the turkey on a tray and rub the skin thoroughly with the cut lemon.
Step 2In a small bowl, mix together half of the olive oil along with the garlic, chili pepper, salt, black pepper and nutmeg. Rub the marinade evenly inside and outside the bird, reserving any that remains. Put the bunch of rosemary in the cavity and truss the bird. Cover it loosely with foil and leave for 1 hour at room temperature.
Step 3Heat the oven to 375 degrees.
Step 4In a large roasting pan, toss the onions with the remaining olive oil and set the turkey on the onions, breast-side-down. Baste the turkey with remaining marinade. Roast it, basting often, for about 1 hour until the back (upper side) of the bird is well-browned. With a large spoon and fork (and maybe the help of another person), turn the turkey breast-side-up. Baste the turkey from time to time and roast until meat starts to shrink from the drumstick bones and the juices run clear, 45 minutes to an hour. A meat thermometer inserted in the thigh should read 160 degrees. If the turkey colors too quickly, tent it loosely with foil. If the onions start to scorch toward the end of roasting, add a cup of chicken broth to the pan. While the turkey roasts, prepare the mushrooms.
Step 1Pick over the mushrooms, trimming tough ends and brushing them to remove any dirt (do not wash them). In a large frying pan, melt the butter over medium heat, then add the mushrooms with 1 teaspoon salt and one-eighth teaspoon pepper. Saute the mushrooms over medium heat, stirring often, about 5 minutes. Sprinkle the garlic and shallots over them and cook until the mushrooms are tender and any liquid they produce has evaporated, another 5 to 10 minutes. Taste and adjust seasoning if desired. The mushrooms can be cooked a day ahead; let them cool, then wrap and refrigerate them. To reheat, place the mushrooms back in the pan over medium heat for 4 to 5 minutes until warmed through, stirring frequently. Stir in the chopped parsley just before serving.
Step 1When the turkey is done, transfer the bird to a tray to catch any juices and cover the bird loosely with foil. Drain any excess fat from the pan, leaving the juices.
Step 2Make the gravy: If the onions and pan juices are not browned, brown them on the stove top over high heat 5 to 10 minutes if necessary. Add the wine to the hot pan, stirring to dissolve any flavorful bits that stick to the bottom of the pan and boil until reduced by about half, about 8 to 10 minutes.
Step 3Meanwhile, boil the chicken broth in a small pan until reduced by half. Add the broth to pan juices and taste: If the flavors are too bland, continue to boil a few more minutes to concentrate the flavors.
Step 4In a small bowl, crush the butter with a fork and work in flour to make a paste. Add any juices from the cooked turkey to the simmering pan juices. Whisk in pieces of the butter, working over the heat so the butter melts and distributing the flour to thicken the gravy evenly. Add butter until the gravy is thickened to the consistency you like. Simmer it 1 to 2 minutes, taste and adjust seasoning. Strain the gravy into a saucepan for reheating and cover. (The turkey and gravy can be cooked a day ahead up to this point; cool them to room temperature, wrap and store in the refrigerator.)
Step 5About 1 1/2 hours before serving, heat oven to 375 degrees and prepare to wrap the turkey in foil. Arrange 2 long strips of foil lengthwise, overlapping slightly, and 1 long strip crosswise across the middle two (make sure each strip is large enough to wrap around the turkey). Unwrap the turkey and place it in the center of the foil. Brush the breast and legs with gravy and wrap very tightly. Set the package in a roasting pan or tray to catch drips and reheat in oven about 1 hour until turkey is steaming and a skewer inserted between the thigh and the body is hot to the touch when withdrawn after 30 seconds. Transfer the turkey to a large, warm platter, cover loosely with foil and keep in a warm place.
Step 6While the turkey is reheating, warm the remaining gravy in the saucepan over medium heat, stirring occasionally.
Step 7In a medium fry pan, reheat the mushrooms over medium heat until warmed, about 5 minutes, stirring frequently.
Step 8Adjust the seasoning for the gravy and pour it into bowls for serving.
Step 9Discard the trussing and rosemary from the turkey. Garnish the platter with the mushrooms. Carry the turkey in triumph to the table.