Preheat the oven to 375°F. Butter a 9x13-inch casserole dish.
In large skillet, melt butter over medium heat. Add onion, celery and garlic. Sauté about 3-4 minutes, until beginning to soften. Add sliced mushrooms to pan and continue to cook, stirring occasionally, until the mushrooms have softened.
Transfer cooked vegetables to large mixing bowl. Add bread cubes to bowl with vegetable mixture. Stir to combine. Pour bread cubes into prepared casserole dish.
In medium bowl, combine broth, eggs, herbs, salt and pepper; mix well. Pour broth mixture evenly over bread and vegetable mixture; gently press bread crumbs down to ensure bread absorbs broth evenly.
Cover with foil and bake 40 minutes. Remove foil, bake 20 minutes more, until browned, warmed through and set. Remove from oven and let cool slightly before serving.