Peel and finely chop the shallots. Sauté them in a knob of butter with a sprig of chopped rosemary.When golden brown, remove a third of them and set them aside in a salad bowl.Add the baby spinach leaves (washed and dried) and toss for 30 seconds.
In a bowl, thoroughly mix the stuffing with the spinach, cranberries, a quarter of the chestnuts, half of the mushrooms, the foie gras cut into small cubes, the egg, salt and pepper.
To prepare the roast
Butterfly the turkey breast with a large knife to create a large cutlet.You can also ask your butcher to do this. Flatten it slightly with a rolling pin. Season with salt and pepper.
Place the sausage-shaped stuffing on one half and roll it up loosely.Tie it with kitchen twine.