Dice brioche into a medium dice and allow to dry in a low oven or overnight at room temperature. Once dry, you will have about 2 cups total.
Melt 1/4 cup (1/2 stick) of butter in a sauté pan. Sweat the celery, pear and onion until translucent and soft. ("Sweating" vegetables means slowly cooking them over low heat until soft but not brown.)
In a second sauté pan, melt the remaining butter and cook sausage gently.Add the cognac and cook the alcohol out. Combine the butter and sausage with the diced brioche, celery and onion mixture, chestnuts, peat, tock in a large bowl and toss gently. Season with salt to taste. Gently add eggs and toss to combine. Finish with chopped herbs, spices and pepper.
Bake in a 9- by 13-inch baking dish at 350 degrees Fahrenheit for 40/45 minutes or until browned and hot throughout.
figs, apples are a great substitution for pears. Fennel can be added.