2) Cut or tear the bread into 2cm cubes and spread it evenly on two baking sheets. Toast the bread in the oven until completely dry and beginning to crisp and brown, about 20 minutes. Transfer to a large mixing bowl.
3) Melt a quarter of the butter in a large frying pan over a medium-high heat. Add the mushrooms and a few pinches of salt and saute, stirring occasionally, until golden brown, about 6 to 8 minutes.
4) Add the celery, onion, another quarter of the butter and the thyme. Once the butter has melted, cook, stirring frequently, until the vegetables have softened, about five minutes. Add the sage and remaining butter. Add the chicken stock to the pan and stir to combine. Season with salt and pepper, to taste.
5) Pour the chicken stock mixture over the bread cubes and toss to combine, until the bread cubes absorb the liquid. Pour the mixture into the greased baking dish and sprinkle with parsley.
6) Bake in the centre of the oven until heated through and the top is golden brown, about 40 minutes. Remove the stuffing from the oven and allow to cool for about 15 minutes before serving.