The day before: Prepare the duck – remove the giblets and neck from the cavity (you can reserve them for the gravy). Clean the duck with wet paper towels then pat dry with dry paper towels (inside and outside). Trim excess fat around the tail. Rub the duck with salt, pepper, and spices. You need to rub it inside, outside, then loosen the skin from the duck breast (without totally detaching it) and rub thoroughly with salt and herbs. Place the duck in a large dish in the fridge, uncovered, overnight, but better for one whole day.
On the day of baking: Take the duck out of the fridge, leave it on the counter for 30-60 minutes to warm up. In the meantime, set the oven to 450°F (230°C / Gas Mark 8), no fan.
Cut the lemon in half. Peel and core the apples, cut into quarters. Put inside the duck (as many as fits).
Use toothpicks to close the cavity, you can also tie the legs together with kitchen twine (this is optional).
Place the duck, breast side down, in a large baking dish (it must be large enough for the whole duck to fit in).
Roast the duck: Put in the oven and bake uncovered for 30 minutes.
Then cover the dish with a lid or wrap it tightly with a piece of aluminum foil. Reduce the temperature to 350°F (180°C / Gas Mark 4) and bake for 1 hour. At the end of this time, start peeling the potatoes, cut them into 1.5-inch (4 cm) chunks. Peel the carrot and cut it into smaller chunks, cut the celery stalk into 4-5 parts.
Turn the duck on the other side (it should be breast-side up now), place the potatoes, carrot, celery, and fresh herbs around the duck.Bake, covered, for 1 hour.
Brown the skin: turn on the broiler setting (or grill setting), place the duck on the top shelf, uncover, and roast for about 5 minutes or until the skin is browned.
Take the duck out of the oven, transfer to a large plate, leave to rest for about 10-15 minutes. You can make the gravy while the duck is resting.
Gravy: Strain the vegetables, leaving the baking liquid in a medium saucepan. Most of this liquid is fat. Try to collect the fat, it will gather at the top of the liquid (it’s more clear and yellow), scoop it with a spoon or a ladle, you can discard it or use it in other recipes. About ¾ cup of brown-colored liquid should be left in the pot. Whisk flour with cold chicken broth, add to the pot with baking liquid. Whisk thoroughly and cook for about 3-5 minutes until slightly thickened. Season with pepper if necessary (it should be already salty enough).
Carve the duck into pieces and serve with roasted potatoes, apples, and gravy.