Defrost the turkey in the fridge overnight if you are using a frozen turkey. Remove the turkey from the refrigerator. Thoroughly clean the turkey, removing giblets, turkey neck, and excess fat. Pat the turkey dry with paper towels.
In a small bowl, combine minced ginger, minced garlic, green onions, Sichuan peppercorn (grind to powder before use), Chinese five-spice powder, dried tangerine peels, Shaoxing cooking wine, oyster sauce, light soy sauce, and brown sugar. Mix well until you have a smooth paste.
Rub the unsalted butter all over the turkey, including under the skin and inside the cavity. Rub half of the marinade mixture over the turkey skin, making sure to get under the skin as well for maximum flavor. Sprinkle salt and black pepper to finish. (You can start to marinate the turkey a couple hours before cooking if you want)
Preheat the oven to 325°F(163°C). Meantime, prepare the sticky rice. Heat a large skillet over medium heat. Add a tablespoon of cooking oil and let it heat. Add carrots, celery, and soaked dried Shiitake mushroom to the hot oil and stir for about 20-30 seconds until fragrant. Then add one tablespoon of the turkey marinade sauce and continue to stir for 10 seconds. Add in the sticky rice to stir fry a few seconds more. Reduce the heat to low to add in the water and let it simmer until the sticky rice turns to an oatmeal-like paste. Add a pinch of salt and turn off the heat.
Stuff the turkey cavity with the sticky rice mixture. Be sure not to pack it too tightly to allow for even cooking.
Place the entire turkey on a roasting rack of a large roasting pan with turkey breast side up. Pour 2 cups of water into the bottom of the pan. Cover the turkey loosely with aluminum foil for the first part of the roasting to prevent the skin from burning.
Roast the turkey in the preheated oven. Estimate the cooking time based on the turkey's weight (about 15 minutes per pound), and mine took about 4 hours and 15 minutes. Remove the foil during the last hour of roasting to allow the skin to brown. Brush the marinade sauce on the turkey every 45 minutes until the skin is golden brown.
Use a meat instant-read thermometer to check the internal temperature. The turkey is done when the thickest part of the thigh reaches 165°F (74°C). Once the turkey reaches the desired temperature, remove it from the oven and let it rest on a cutting board for at least 30 minutes.
Carve the turkey and serve with the flavorful sticky rice stuffing. Enjoy!