If you haven't already, cut or tear day-old bread into 1/2- to 3/4-inch cubes. Spread on a baking sheet and toast in a 325°F (160°C) oven for 10–12 minutes until dry but not browned. Transfer to a large mixing bowl.

Sauté vegetables

In a large skillet over medium heat, melt 6 tablespoons unsalted butter. Add the finely chopped onion and celery and cook, stirring occasionally, until softened and translucent, about 6–8 minutes. Add the sliced mushrooms (if using) and cook another 4–5 minutes until their liquid has mostly evaporated. Stir in the minced garlic, chopped sage, parsley and thyme; cook 1 minute until fragrant.

Season and combine

Stir the cooked vegetables and herbs into the bowl with the toasted bread cubes. Add the dried cranberries and toasted nuts if using. Sprinkle the kosher salt and freshly ground black pepper over the bread mixture and toss gently to combine.

Make custard and moisten bread

Whisk together the warm chicken or vegetable stock, lightly beaten eggs and heavy cream. Pour the liquid evenly over the bread and vegetable mixture, tossing gently with a large spoon or your hands to ensure all bread is moistened but not soupy. Let the mixture sit 10 minutes to absorb; if it seems dry, add up to an additional 1/4 cup warm stock.

Baking & Finishing

Transfer to baking dish

Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish or a similarly sized casserole with butter. Transfer the moistened stuffing mixture into the dish, pressing gently to even the surface.

Dot with butter

Drizzle or dot the top of the stuffing with the 2 tablespoons melted butter to encourage browning.

Bake

Bake uncovered for 30–40 minutes, until the top is golden brown and the interior is set. If you prefer a very crisp top, bake an additional 5–10 minutes, watching to prevent burning. If the top browns too quickly, tent loosely with foil.

Rest and garnish

Remove from the oven and let the stuffing rest 5–10 minutes before serving. Sprinkle with chopped fresh parsley and serve warm alongside roasted poultry or as a standalone side.