This easy breakfast casserole is infinitely adaptable! Use your favorite seasonings, vegetables, meats, cheeses, or make it vegetarian. The best part is that you can prepare it ahead of time so breakfast is a breeze in the morning.
Today’s breakfast casserole recipe comes from my dear friend Kristen. She made it for us when we visited last month. As I gobbled it down, I couldn’t stop saying “I have to share this on my blog, I have to share this on my blog, I have share this on my blog.”
As it turns out, this is something Kristen makes on the regular. And I understand why! Besides taste, this breakfast casserole is pretty impressive in the health category. Full of protein, packed with vegetables. Not only that, it’s so easy to make and adaptable to whatever veggies, cheeses, meats, seasonings you love/have on hand. Confession. I’ve made this 4 times in 3 weeks.
↑ ↑ Soooo much texture and flavor!
This is a big breakfast casserole. I’m talking 12 huge servings, so it’s perfect for dinner or breakfast/lunch the next day. I reheat it in the microwave and top it with hot sauce. Delicious! I took a bunch of step-by-step photos so instead of displaying them all above the recipe, I included them below along with more detailed instructions for you.
Entertaining? If you’re entertaining, pair this breakfast casserole with slow cooker cinnamon rolls or my overnight cinnamon rolls. Both homemade and both VERY easy, especially if you’re a yeast beginner.
Easy Make-Ahead Breakfast Casserole
Makes excellent leftovers for breakfast, lunch, and dinner during the week! Make sure to read the recipe notes and check out all the step-by-step pictures below this recipe before you begin.
- 3/4 pound uncooked sausage, casings removed*
- optional: 1 teaspoon dried rosemary to give the sausage more flavor
- 2 bell peppers, diced (any color you prefer; about 2 cups)
- 1 cup sliced mushrooms
- 1 cup fresh spinach
- 1/2 medium yellow onion, diced
- 1 teaspoon minced garlic
- salt and fresh ground black pepper
- 4 slices day-old bread (gluten free, whole wheat, white, sourdough, any kind you like)
- 10 large eggs
- 1/2 cup milk (I use almond milk, any milk works)
- 1/2 cup shredded cheese*
- Set a large skillet over medium heat and coat it with nonstick spray or a drizzle of olive oil. Place sausage in the skillet and begin to break it up with a spatula or fork. Stir in the rosemary and brown the sausage, about 6-7 minutes.
- Meanwhile, set a 2nd skillet over medium heat and coat it with nonstick spray or a drizzle of olive oil. (If you have a skillet large enough to fit both the sausage and veggies, you can just add the veggies to the sausage that is browning in step 1.) Add the peppers, mushrooms, spinach, onion, garlic, and a sprinkle each of salt and pepper. Begin stirring and cooking the veggies down until tender, about 6-8 minutes.
- Set sausage and veggies aside.
- Generously grease a 9x13 baking pan. Break the bread into pieces and place in the pan in an even layer.
- In a large bowl, whisk the eggs, milk, and 1/4 cup shredded cheese together. Pour half of this egg mixture over the bread. Top with the sausage and vegetables, then the remaining egg mixture and remaining 1/4 cup cheese. Add a sprinkle of salt and pepper on top.
- Cover casserole with plastic wrap or aluminum foil and refrigerate for 2 hours or overnight-- or up to 1 day. Allow it to come to room temperature before baking.
- Preheat the oven to 375°F (191°C). Bake the casserole, uncovered, until the top is golden, edges are crisp, and a toothpick inserted in the center comes out clean-- about 40-45 minutes. I like mine on the super crisp side, so I bake it for around 45-50 minutes. Allow to cool for 10 minutes, then slice and serve. Tastes awesome with hot sauce on top.
- Leftovers keep well in the refrigerator for up to 5 days. Reheat in the microwave to your liking.
Make ahead tip/Freezing instructions: Obviously this is a make ahead recipe! However, you can brown the sausage and cook down the veggies up to 2 days in advance-- simply put the two in a tupperware in the refrigerator until ready to use in the recipe. Also, you can freeze this breakfast casserole. Prepare through step 5, then cover the casserole with plastic wrap, then a layer of aluminum foil. Freeze for up to 3 months. Allow to thaw overnight in the refrigerator. Bring to room temperature, then continue with step 7.
The onion, garlic, salt, pepper, and cheese are key to great flavor! Don't leave them out.
- Instead of sausage, try browning ground turkey, ground beef, or ground chicken instead. Or use ham. Or cooked shredded chicken. Vegetarians: You can leave out the meat. Just an extra cup (or so) of veggies in its place.
- I usually use shredded pepper jack cheese-- other varieties I love for this breakfast casserole are mozzarella, smoked gouda, swiss, and cheddar.
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How to Make Breakfast Casserole
Vegetables: Gather veggies like colorful peppers, mushrooms, and spinach. I’ve done this with broccoli/peppers, kale/mushrooms, and spinach/zucchini. Try to stick to 3-4 cups veggies total. Cook the veggies down with a little garlic, onion, salt, and pepper. Those last 4 ingredients are where all the flavor comes from.
Meat: We like a little meat in the casserole, so I add sausage. Kristen usually uses turkey sausage, so go ahead and use that if you prefer. Instead of sausage, try using ground turkey, ground beef, or ground chicken instead. You can also use diced pre-cooked ham or cooked shredded chicken. You don’t need to pre-cook either of those options.
I brown the sausage with some rosemary to give a little flavor. You can cook down the veggies and brown the sausage in 1 giant skillet if that’s easier for you.
- Vegetarians: You can leave out the meat. Just use some more veggies in its place!
Bread: Grab your favorite crusty bread and tear it into little pieces. The bread will be the bottom of the casserole. It soaks up some of the egg and gives the egg casserole texture. It is SO good! Otherwise, you’d just be eating a quiche of sorts. I’ve been using gluten free bread for my sandwiches lately, so if you don’t eat gluten, you can use your favorite GF variety. Or you can certainly use wheat, sourdough, white, rye, whatever. You’ll need about 4 slices of bread.
Eggs, milk, & cheese: Whisk the eggs with a little milk and cheese. Like the veggies and meat, use whatever cheese you like best. I’ve been using pepper jack cheese for its flavor but I’ve done everything from cheddar to smoked gouda and swiss. Half of the egg mixture goes on top of the bread, then sausage and veggies, then the remaining egg mixture.
Once the eggs are poured on top of it all, you can refrigerate the casserole overnight. Wake up and all you have to do is throw it in the oven. When we visited Kristen, the morning was totally no-fuss; all she did was brew some coffee and cut up fresh fruit as the casserole cooked. Enjoy!
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