Step 1

Heat the oven and prepare the baking dish. Arrange 2 racks to divide the oven into thirds and heat to 350°F. Meanwhile, coat a 9x13-inch or other 3-quart baking dish with butter and set aside.

Step 2

Toast the bread dry. Divide the bread cubes between 2 rimmed baking sheets and spread into a single layer. Toast until the bread is completely dry, 10 to 12 minutes. Set aside to cool.

Step 3

Cook the leek and celery until tender. Melt 4 tablespoons of the butter in a 12-inch high-sided skillet over medium heat. Add the leek and celery and cook, stirring occasionally, until beginning to soften, 6 to 7 minutes.

Step 4

Add the mushrooms and herbs. Increase the heat to medium-high. Add the mushrooms, sage, thyme, black pepper, and 1 1/4 teaspoons of the salt. Cook until the mushrooms are golden-brown, tender, and any liquid released is almost evaporated, 15 to 18 minutes.

Step 5

Mix the bread with the mushroom mixture. Transfer the mushroom mixture to a very large bowl. Add the bread cubes and parsley, and toss to combine.

Step 6

Whisk the eggs and broth, and mix in. Place the broth, eggs, and remaining 1/4 teaspoon salt in a medium bowl or large liquid measuring cup and whisk to combine. Pour over bread and mushroom mixture and use your hands or a large spoon to gently toss until all the bread is evenly moistened.

Step 7

Transfer to the baking dish and top with butter. Transfer to prepared baking dish and spread into an even layer. Cut the remaining 2 tablespoons of butter into small pieces and dot the top of the stuffing with the butter.

Step 8

Cover and bake. Cover the baking dish tightly with a lightly buttered piece of aluminum foil. Bake until warmed through and slightly puffed, 20 to 25 minutes.

Step 9

Uncover and bake at 425°F until crispy. Increase the oven temperature to 425°F. Uncover and bake until the top is golden-brown and crisp, 20 to 25 minutes more. Sprinkle with more thyme leaves before serving.