Preheat your oven to 350°F and grease a 13x9-inch casserole dish.

In a heavy-bottomed skillet, brown the bread crumbs in 2 tablespoons of butter over medium heat for about 5 minutes until golden brown. Set aside to cool slightly.

Melt ½ cup of butter in a large skillet over medium heat. Add the diced celery, chopped onion, and fresh parsley. Sauté for approximately 5 minutes until tender and aromatic.

Add the cubed bread to the skillet with the sautéed vegetables. Toss to combine and sprinkle in salt, pepper, and poultry seasoning. Transfer to the greased casserole dish and drizzle with chicken broth.

Melt 1 cup of butter in a separate skillet. Whisk in ½ cup of flour until combined. Gradually add 4 cups of chicken broth and 1 cup of milk, whisking until thickened, about 10 minutes.

In a small bowl, whisk the eggs. To temper, add 1 cup of the hot broth mixture slowly while whisking constantly. Pour back into the remaining broth and cook over low heat for about 3 minutes.

Pour the sauce over the bread mixture, layer cubed chicken on top, and sprinkle browned breadcrumbs for a crispy finish.

Bake in the preheated oven for 30-35 minutes until bubbly and the center reaches 160°F.