1. Grease a 9×13-inch baking dish thoroughly with butter or cooking spray.

2. Cube bread into 1-inch pieces and let sit uncovered 2-3 hours to dry slightly, or dry in 200°F oven for 10 minutes.

3. Heat large skillet over medium-high heat. Add crumbled sausage and cook, breaking into small pieces, until browned and cooked through (6-8 minutes, reaching 165°F internal temp). Drain excess fat and transfer to paper towel-lined plate.

4. In same skillet, sauté diced bell peppers and onions until softened (5 minutes). Add spinach if using during last minute. Season with salt and pepper.

5. In large bowl, whisk together eggs, milk, cream, salt, pepper, garlic powder, and paprika until well combined and slightly frothy.

6. Spread cubed bread evenly in prepared baking dish. Top with cooked sausage, sautéed vegetables, and 1.5 cups shredded cheese, distributing evenly.

7. Pour egg mixture over everything, ensuring all bread is moistened. Press down gently with spatula to help absorption. Sprinkle remaining 1/2 cup cheese on top.

8. For immediate baking: Let sit 15 minutes at room temperature. For make-ahead: Cover tightly with plastic wrap and refrigerate up to 24 hours.

9. Preheat oven to 350°F. If baking from refrigerator, let casserole sit at room temperature 20-30 minutes while oven preheats.

10. Bake uncovered 45-55 minutes until center is set, edges golden, and internal temperature reaches 160°F. If top browns too quickly, tent with foil.

11. Let rest 10-15 minutes before slicing into squares and serving.