Preheat oven to 225°F. Line a baking sheet with a lip with parchment paper.
Arrange bread cubes on the baking sheet and bake for 45 minutes. Turn occasionally so the croutons evenly cook. After 45 minutes, they should be golden-brown; if not, continue to cook for a few minutes until they are. Set aside to cool.
6 cups Bread
While the croutons bake, add porcini mushrooms to a small bowl. Cover with hot water and set aside to steep for 20 minutes.
½ ounce Dried porcini mushrooms
Chop bacon, leek, and onion into even sizes.
1 cup Leek, ⅓ cup Bacon, 1 medium White onion
Turn the oven up to 350°F and grease a large (9-by-13 inch) roasting dish. If you don't have a large dish, you can use 2 smaller dishes with the stuffing evenly divided between them.
Melt butter in a skillet over medium-high heat and add onions. Saute until softened, then add the leek and continue cooking.
½ stick Butter, 1 medium White onion, 1 cup Leek
Move vegetables to the side of the pan and add bacon. Cook, turning frequently, for several minutes. Remove the pan from the heat once cooked.
⅓ cup Bacon
Strain the mushrooms but reserve the liquid. Chop and add to the skillet with walnuts and thyme, and stir.
½ ounce Dried porcini mushrooms, ½ cup Walnuts, 2 Tablespoons Fresh thyme leaves
Place croutons in a large mixing bowl with the vegetable and bacon mix. Using a large spoon, mix so the flavors are fully combined.
6 cups Bread
Filter mushroom water through a fine-meshed sieve to remove grit, then pour it into the vegetable stock (optional).
1 cup Vegetable stock
Add all the liquid to the stuffing mix. Toss briefly, just enough to evenly coat everything in the bowl, but not enough to break the bread. Taste, then season with salt and pepper as desired.
Transfer stuffing to the roasting dish and cover with foil. Bake for 20 minutes, then remove the foil and bake another 10 minutes (up to 20 minutes for a crisper finish).
Serve, and enjoy!