Preheat oven to 350 degrees. Butter a 9x13 baking dish and set aside.
Place the torn or cut bread onto a baking sheet and toast in the oven for 15 minutes until its just turning golden brown.
In a large pan, melt 4 tbsp of butter. Once melted add the slices mushrooms and sauté until cooked down. Add the onions, celery and fresh thyme. Once the onions are translucent, add the chicken broth to the pan, season with salt and pepper and transfer to a large bowl. In the same skillet, add 2 more tbsp of butter and sauté the sausage until cooked through. Remove from heat.
Transfer the toasted bread cubes to the baking dish. Add the sausage. Cover with the chicken broth mixture and toss to combine. Season with salt and pepper.
Bake for 45 minutes, until the top is golden brown. Remove from oven and serve.