When you want an egg dish to feed a crowd or make enough breakfast for the week, breakfast casseroles are just the ticket. Eggs hold together whatever ingredients you want to put in the baking dish, and in this case it's a filling combination of frozen diced potatoes, savory sausage, a whole bag of baby spinach, and, of course, a few handfuls of shredded cheese. This casserole is a bit like a diner omelette and breakfast potatoes all in one dish, and it's nice to start the day knowing you've already had a serving of greens!
This is a pretty classic breakfast casserole that starts off with a quick sauté of breakfast sausage (use your favorite, whether pork or poultry), sweet onion, oregano, and a bag of baby spinach. Layer it over frozen diced potatoes, then pour the beaten eggs and milk right over the top before finishing it off with some shredded Italian cheeses. Then bake the casserole until it's custardy with a nicely browned top.
This dish has lots of make-ahead options. Sauté the filling or completely assemble the night before, then bake the next morning. You can even freeze the unbaked casserole — it'll just need some extra baking time, but no more more prep time. Breakfast or brunch is just a bake away.
Sausage and Greens Breakfast Casserole
1 pound frozen diced potatoes (about 4 cups, do not thaw)
1 tablespoon olive oil, plus more for the baking dish
1 pound uncooked breakfast sausage, casings removed
1 medium yellow onion, diced
1 1/2 teaspoons dried oregano
5 ounces baby spinach (about 5 packed cups)
8 large eggs
1 1/2 cups whole or 2% milk
1 1/2 teaspoons kosher salt
1/4 teaspoon freshly ground black pepper
2 cups shredded Italian blend cheese (such as Parmesan, mozzarella, provolone)
Arrange a rack in the middle of the oven and heat to 350°F. Coat a 9x13-inch baking dish with olive oil. Add the potatoes and spread into an an even layer; set aside.
Heat the 1 tablespoon of oil in a large frying pan over medium-high heat until shimmering. Add the sausage, onion, and oregano and cook, breaking up the meat into small pieces with a wooden spoon, until the sausage is cooked through and the onions are tender, about 8 minutes. Add the spinach and toss until wilted and almost all of the liquid is evaporated, about 3 minutes. Transfer to the baking dish and spread into an even layer over the potatoes.
Whisk the eggs, milk, salt, and pepper together in a large bowl until the eggs are completely broken up and incorporated. Pour over the ingredients in the baking dish. Sprinkle evenly with the cheese.
Bake until the edges are golden-brown and a knife inserted in the center comes out clean, about 50 minutes. Let cool for 5 minutes before slicing and serving.
- Make ahead: The casserole can be assembled, covered with aluminum foil, and chilled overnight before baking. Uncover before baking.
- Freezing: The casserole can also be frozen unbaked. Cover tightly with aluminum foil, wrap in plastic wrap, and freeze for up to 3 months. Thaw overnight in the refrigerator, then proceed with baking uncovered as instructed. Depending on how frozen the casserole still is, it may take up to 1 1/2 hours baking time, check after 1 hour.
- Storage: Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.