Preheat your oven to 350°F and butter a 9x13 inch baking dish generously. Arrange cubed bread evenly across the bottom, creating a sturdy foundation for custard absorption.

Heat butter in a large skillet over medium heat and sauté diced onions until softened, about three minutes. Add sliced chicken apple sausage, cooking until edges brown lightly and flavors marry beautifully, approximately five minutes total.

Stir in diced apples and sliced mushrooms, cooking until apples soften slightly and mushrooms release their moisture, roughly four minutes. This step develops the savory-sweet foundation that makes apple sausage casserole so memorable for crowd brunch occasions.

In a large bowl, whisk together eggs, milk, chicken broth, dried sage, thyme, salt, and black pepper until completely smooth. Pour this custard mixture over bread cubes carefully, allowing ten minutes for complete absorption before adding cooked sausage mixture.

Distribute cooked sausage, apples, and mushrooms evenly over bread and custard layer. Sprinkle shredded cheddar cheese across the entire surface uniformly for golden melting during baking.

Toss chopped pecans with maple syrup in a small bowl, then scatter over cheese layer creating textured topping. Bake uncovered for 35 minutes until center sets and top turns golden brown, then remove and cool five minutes before serving.