Double-duty casserole! Prepare the night before and then bake the next morning for a delightful breakfast or brunch! Cut the leftovers into squares and wrap up for ready-to-go mid-week lunches.
In a large sauté pan, heat the oil and add the onion. Cook for 5 minutes. Add the tomatoes and mushrooms and cook until starting to brown. Season with salt and pepper to taste. Start adding the spinach a little at a time until all cooked down. Set aside to cool.
In a large bowl, whisk the eggs, and add in the half and half, both cheeses and Worcestershire sauce. Season with salt and pepper and mix well. Add in the cooked sausage along with the veggie mixture and combine well.
Lightly grease a 9×12 baking dish with butter. Add half of the bread cubes and then pour over it half the egg mixture. Repeat and make sure all bread is covered. Let it sit for at least 1 hour or overnight. Bake approximately 1 hour in a 375° preheated oven until firm.
Let casserole rest before cutting.