In a skillet over medium heat, cook the sausage until it is browned and cooked through, breaking it into small pieces as it cooks. Drain any excess fat and set aside to cool slightly.
In a large mixing bowl, whisk together the eggs, milk, sour cream French onion dip, salt, and pepper until well combined.
In the baking dish, layer the cubed French bread evenly across the bottom. Sprinkle the cooked sausage over the bread, followed by a generous layer of Cheddar cheese.
Pour the egg mixture evenly over the layered bread, sausage, and cheese. Make sure all the bread is soaked in the egg mixture. Press down gently with a spatula to ensure everything is well distributed.
Cover the dish with plastic wrap and refrigerate for at least 30 minutes or overnight.
Preheat your oven to 350°F (175°C). Remove the casserole from the refrigerator and let it sit at room temperature for about 10 minutes. Bake uncovered for 45-50 minutes, or until the top is golden brown and the eggs are set.
Allow the casserole to cool for a few minutes before slicing. Serve warm, garnished with fresh herbs if desired.