1. Preheat oven to 375°. Place bread cubes on a large rimmed baking sheet. Melt 1/4 cup butter in a large skillet over low heat. Drizzle melted butter over bread cubes; toss to coat. Bake at 375° for 20 minutes or until golden, stirring halfway through. Transfer cubes to a large bowl.
2. Melt 3 Tbsp. butter in skillet over medium-high heat. Add onion and next 4 ingredients to skillet; sauté 12 minutes or until tender. Add mushroom mixture to bread cubes.
3. Melt remaining 1 Tbsp. butter in skillet. Add apple; sauté 4 minutes or until golden. Add apple to bread mixture.
4. Whisk together cream and next 4 ingredients. Pour over bread mixture; toss well. Pour bread mixture into a greased 13- x 9-inch baking dish. Cover and chill at least 8 hours.
5. Preheat oven to 350°. Uncover casserole and bake at 350° for 1 hour and 10 minutes or until set and lightly browned. Let stand 15 minutes.