Preheat oven to 350°F (175°C). Spray a large (9 x 13-inch) baking dish with nonstick spray, then set aside for later.
Divide cubed bread between 2 large baking sheets. Bake for 10 minutes, then flip. Cook for another 5 to 10 minutes, or until edges are crunchy. Set aside.
While bread cooks, melt butter in a large frying pan over medium heat.
When butter is hot, add celery and onions, and season with salt and pepper. Cook until starting to turn translucent, stirring frequently (about 7 to 10 minutes).
Add mushrooms and cook (stirring frequently) until any liquid has evaporated and mushrooms are starting to brown (about 10 to 15 minutes).
Stir in chestnuts, then cook (stirring frequently) until they start to brown (about 5 minutes).
Remove pan from heat, then stir in parsley, sage, and thyme. Season generously with salt and pepper to taste.
Place dried bread cubes in a large bowl. Top with sautéed veggies and egg.
Add broth a little at a time, stirring well after each addition. Add just enough broth so that the stuffing is moistened, but not soggy. (You may have leftover broth, or you may need more, depending on your bread.)
Transfer stuffing to baking dish, then bake until hot and lightly browned on top (about 35 to 40 minutes).
Serve stuffing hot. Enjoy!
Notes
Chestnuts - To save time, I used packaged chestnuts (three 3.5 ounce / 100 gram packages), which were already roasted and peeled. If you'd prefer to start with raw chestnuts, check out these cooking tips.Adjusting the Oven Temp - If you're cooking something else at a similar temperature that's a little lower or higher, it's fine to cook the stuffing at the same temp. Just watch the stuffing closely, and remember to adjust the cooking time up or down, as needed.Make Ahead of Time - To prep the recipe in advance, cook the veggies and toast the bread, then refrigerate the veggies in an airtight container, and store the bread in a separate airtight container at room temp. On the big day, mix the veggies and bread together, along with the egg and broth. Bake according to directions above, keeping in mind that it may take slightly longer since the veggies are cold.More - Make sure to read the info before this recipe card for helpful tips, variations, servings suggestions, related recipes, and more!