Start by gathering all your ingredients. Remove the crusts from the Italian bread and cube it into bite-sized pieces. Set it aside.
In a skillet over medium heat, add the breakfast sausage. Break it up with a spatula and cook until it’s browned and fully cooked through, about 5-7 minutes. Drain any excess grease and set aside to cool slightly.
In a large mixing bowl, crack the 9 eggs and pour in 1 cup of milk. Add the 1.5 teaspoons of salt. Whisk together until the mixture is well combined and slightly frothy.
Add the cubed Italian bread to the egg mixture, followed by the cooked sausage, shredded Swiss cheese, and shredded cheddar cheese. Gently fold the ingredients together until the bread is evenly coated with the egg mixture.
Preheat your oven to 350°F (175°C). Grease your 9x13-inch baking dish with cooking spray or butter. Pour the combined mixture into the dish, spreading it evenly.
Place the casserole in the preheated oven and bake for 30-35 minutes, or until the top is golden brown and the eggs are set in the center. A toothpick inserted should come out clean.
Once baked, remove the casserole from the oven and allow it to cool for a few minutes before slicing. Serve warm and enjoy!