How to Make It
Heat oven to 400° F.
Butter a deep 3-quart casserole dish.
Place the bread on a rimmed baking sheet and toast until golden, 10 minutes. Transfer to a large bowl.
Melt the butter in a large saucepan over medium-high heat. Add the onions, celery, and 1/2 teaspoon each salt and pepper and cook, stirring occasionally, until softened, 8 to 10 minutes. Stir in the apples and cook for 2 minutes. Add the broth and bring to a boil.
Add the vegetable mixture, parsley, and sage to the bread and toss to combine. Mix in the eggs. Transfer to the prepared dish and cover loosely with buttered foil.
Bake for 30 minutes. Uncover and bake until golden, 12 to 15 minutes.