- 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 9×13-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.