Preheat oven to 350°F (175°C) and grease a 9x13 inch baking dish with butter.
In a large skillet, melt the 1/2 cup of butter over medium heat.
Add the onions and celery to the skillet and sauté until softened and translucent, approximately 8 to 10 minutes.
Add the garlic, sage, rosemary, and thyme to the skillet and cook for 1 minute until fragrant.
Place the dried sourdough cubes in a large mixing bowl.
Pour the sautéed aromatics and butter over the bread cubes.
In a medium bowl, whisk together the chicken stock, beaten eggs, salt, and pepper.
Gradually pour the stock mixture over the bread, tossing gently with a large spoon until the liquid is absorbed and bread is evenly moistened.
Fold in the chopped parsley.
Transfer the mixture to the prepared baking dish and spread evenly.
Cover the dish with aluminum foil and bake for 20 minutes.
Remove the foil and continue baking for 25 minutes or until the top is golden brown and the internal temperature reaches 160°F (71°C).