1) Cube bread up into relatively large pieces and toast it in a 300 degree oven until it’s super-crispy and dry for about 20-30 minutes. Give it a quick stir halfway through just to make sure it’s cooking/drying evenly.
2) Cut an X on all of chestnuts and roast them (you can do it at the same time you are toasting your bread) for about 20 minutes or until the shell peels back nicely on each chestnut.
3) When they are roasted, halve each nut and then handle each half basically like a clove of garlic. Gently smash it with the side of a knife, the chestnut will pop right out. Do that for each one.
4) Take the casings off sausage and cook over medium-high heat in a large skillet. If sausage is on the leaner side, you might need to add a tablespoon or two of oil just to help it out.
5) After it cooks for a few minutes and starts to brown, add diced onion to the pan.
6) When the sausage is completely cooked and the onion is translucent, add celery and cook for just a few more minutes.
7) Toss all of this stuff in a bowl with your roasted chestnuts. Add other aromatics (herbs) and flavor ingredients to the sausage mixture and then toss that all together with your bread mixture.
8) Stir it together well to make sure the bread soaks up as much moisture as possible from the sausage and onion.
9) Add stock and butter in 1/2 cup batches and stir well after each batch (approximately 2.5 Cups of stock). Add a big pinch of salt and pepper.
10) Pour stuffing mixture in a 9 x 13 pan.
11) Bake at 350 degrees with foil cover for 30 minutes and then uncovered for 30 minutes, stirring every 15 minutes.