Cut the sourdough bread into 3/4-1-inch (2-2.5-cm) cubes and spread them in a single layer on one or two large baking sheets.
20 ounces dried sourdough bread
To dry the bread at room temperature, leave the cubes uncovered for 1-2 days, tossing once or twice, until completely dry and crisp.
For the oven method, preheat the oven to 250°F (120°C). Spread the bread cubes evenly over the baking sheets and bake for 45-60 minutes, tossing once or twice, until dry and crisp throughout. Let the bread cool completely.
Once the bread is completely dry, weigh out 20 ounces (567 grams) for the recipe. Weigh the bread after drying because it loses moisture as it dries.
Preheat the oven to 350°F (175°C). Lightly butter or spray a 9x13-inch (23x33-cm) baking dish.
Melt 4 tablespoons (56 grams) of the butter in a large skillet or Dutch oven over medium heat. Add the onion and celery and cook for 7-9 minutes, stirring occasionally, until softened.
0.25 cup unsalted butter,, 2 1/2 cups finely diced yellow onion, about 2 1/2 medium onions, 2 cups finely diced celery, about 4-5 stalks
Add the garlic, parsley, sage, rosemary, thyme, poultry seasoning, salt and black pepper. Cook for another 1-2 minutes, until the garlic and herbs are fragrant.
4 cloves garlic, 1/2 cup finely chopped fresh parsley, plus more for garnish, 2 1/2 tablespoons finely chopped fresh sage, 2 tablespoons finely chopped fresh rosemary, 2 tablespoons finely chopped fresh thyme, 2 teaspoons poultry seasoning, 1 1/2 teaspoons kosher salt, or to taste, 1/2 teaspoon freshly ground black pepper, or to taste
Remove the skillet from the heat. Add the remaining 8 tablespoons (113 grams) butter and stir until completely melted into the warm vegetable and herb mixture.
0.5 cup unsalted butter,
Place the dried bread cubes in a very large mixing bowl. Pour the warm butter and vegetable mixture over the bread and gently toss until evenly coated.
Whisk together the eggs and chicken or turkey broth in a separate bowl or large measuring cup.
2 large eggs, 2 1/2 cups chicken or turkey broth
Slowly pour the broth and egg mixture over the bread, gently tossing between additions so the liquid is evenly distributed. Continue until the bread is thoroughly moistened but still holds its shape. If you prefer a particularly moist stuffing, add up to another 1/4 cup (60 grams) broth as needed.
Transfer the stuffing to the prepared baking dish and gently spread it into an even layer. Do not pack it down.
Cover the baking dish tightly with aluminum foil and bake for 30 minutes.
Remove the foil and continue baking for 25-30 minutes, or until the top is golden brown and crisp and the center reaches 165°F (74°C).
Let the stuffing rest for 5-10 minutes before serving. Garnish with additional fresh parsley or herbs, if desired.