High Protein Breakfast Casserole

This protein-packed breakfast casserole has been my weekend lifesaver for years. Loaded with savory sausage, colorful vegetables, and fluffy eggs, it's the perfect make-ahead breakfast that keeps my family satisfied until lunchtime.

I first created this recipe when hosting a holiday brunch for my extended family. Everyone asked for seconds, and now it's become our traditional Christmas morning breakfast while we open gifts.

Ingredients

• Olive oil adds a subtle flavor base and prevents sticking. Look for extra virgin for best results.
• Breakfast sausage provides savory protein. Choose high quality with minimal fillers for best flavor.
• Onion and bell pepper create a flavorful aromatic base. Select firm vegetables with vibrant colors.
• Spinach and mushrooms add nutrition and earthy flavor. Baby spinach works best as it wilts quickly.
• Large eggs provide structure and protein. Pasture raised eggs offer richer color and flavor.
• Milk creates a fluffy texture. Whole milk yields the creamiest results, but any variety works.
• Salt, pepper, garlic powder and paprika create a balanced seasoning blend. Fresh ground pepper makes a noticeable difference.
• Cheddar cheese adds richness and a golden top. Freshly grated melts more smoothly than pre shredded.
• Bread, potatoes or hash browns add substance and texture. Day old bread works perfectly.

Step-by-Step Instructions

Prepare Your Oven

Preheat your oven to 375°F ensuring it reaches full temperature. Thoroughly grease your 9×13 baking dish with cooking spray or butter, getting into all corners to prevent sticking.

Cook The Base

Heat olive oil in a large skillet over medium heat until shimmering. Add your cooked sausage, chopped onion, and bell pepper, sautéing for exactly 5 minutes until onions become translucent and peppers soften slightly. Stir occasionally to prevent burning.

Add The Greens

Incorporate chopped spinach and mushrooms into the hot skillet. Cook for precisely 2 minutes while stirring frequently. The spinach should wilt completely but still maintain its bright green color. Remove the pan from heat immediately to prevent overcooking.

Create The Egg Mixture

In a large bowl, vigorously whisk the eggs and milk until completely combined and slightly frothy. This typically takes about 30 seconds of continuous whisking. Add salt, pepper, garlic powder, and paprika, whisking again to evenly distribute the seasonings.

Combine Components

Gently fold shredded cheese and your choice of bread cubes, potatoes or hash browns into the egg mixture using a rubber spatula. Use a folding motion rather than stirring to maintain air in the eggs for a fluffier result.

Complete The Mixture

Add the sautéed vegetable and meat mixture to your egg bowl. Fold everything together with gentle motions until evenly distributed but not overmixed. The mixture should look colorful with distinct ingredients visible.

Bake To Perfection

Pour the entire mixture into your prepared baking dish, spreading it evenly to the corners. Place in the center rack of your preheated oven and bake for 30 minutes. Check for doneness by inserting a knife in the center which should come out clean. If needed, bake for up to 15 more minutes until golden brown and set.

Rest Before Serving

Allow the casserole to rest for a full 5 10 minutes before cutting. This crucial step lets the eggs fully set for clean slices. Cut into 8 equal portions and serve while still warm.

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My absolute favorite ingredient in this casserole is the combination of sautéed mushrooms and spinach. My daughter used to pick out the spinach until I started finely chopping it to blend in with everything else. Now she requests extra veggies in her portion which feels like a parenting win.

Make Ahead Magic

This breakfast casserole shines as a make ahead meal. Prepare everything the night before, cover tightly with plastic wrap, and refrigerate overnight. In the morning, remove from the refrigerator while preheating the oven, then bake as directed, adding 5 7 minutes to the cooking time. The flavors actually develop and meld overnight, resulting in an even more delicious breakfast with minimal morning effort.

Perfect Pairings

Serve this protein rich casserole with a light side to balance the meal. Fresh fruit salad provides a sweet contrast to the savory flavors. For a special brunch, add mimosas or a spicy bloody mary. If serving for dinner, pair with a simple green salad dressed with vinaigrette. The casserole stands well on its own but becomes a complete meal with thoughtful accompaniments.

Storage Solutions

For refrigerator storage, cool the casserole completely before covering with plastic wrap or transferring to airtight containers. It will maintain quality for 3 4 days. To freeze, cut into individual portions, wrap each in plastic wrap, then foil, and freeze for up to 3 months. Thaw overnight in the refrigerator before reheating. For best results, reheat covered in a 325°F oven until warmed through, about 15 minutes, or microwave individual portions for 1 2 minutes.

Dietary Adaptations

This versatile recipe easily accommodates nearly any dietary need. For keto or low carb, substitute the starchy component with riced cauliflower or additional vegetables. Make it dairy free by using plant based milk and cheese alternatives without compromising texture. For vegetarians, replace the sausage with plant based alternatives or simply double the vegetables. Those with gluten sensitivities can use potatoes instead of bread or select certified gluten free bread cubes. The core recipe maintains its delicious flavor profile regardless of these modifications.

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Common Recipe Questions

→ Can I prepare this breakfast casserole ahead of time?

Yes, you can assemble the entire casserole the night before, cover it tightly with plastic wrap, and refrigerate overnight. In the morning, remove it from the refrigerator while you preheat the oven, then bake as directed, possibly adding a few extra minutes to the cooking time since it will be cold from the refrigerator.

→ How do I know when the breakfast casserole is fully cooked?

The casserole is fully cooked when the center is set and doesn't jiggle when gently shaken. The top should be golden brown, and a knife inserted into the center should come out clean without any runny egg mixture. The internal temperature should reach 160°F (71°C) for food safety.

→ How long will leftover breakfast casserole keep?

Leftover breakfast casserole can be stored in an airtight container in the refrigerator for 3-4 days. You can reheat individual portions in the microwave for 1-2 minutes or until heated through. For best quality, don't freeze the casserole with potatoes or hash browns, as they can become watery when thawed.

→ Can I make this breakfast casserole vegetarian?

Absolutely! Simply omit the breakfast sausage and substitute with crumbled tofu, tempeh, or additional vegetables. You could also add plant-based protein alternatives designed to mimic breakfast sausage. Increase the vegetables by about 1-2 cups to maintain volume and add extra flavor with herbs and spices.

→ What can I serve with this breakfast casserole?

This protein-packed casserole is a complete meal on its own, but pairs wonderfully with fresh fruit, yogurt parfaits, or a light green salad for brunch. For a heartier offering, serve with toast, breakfast potatoes (if not already in the casserole), or warm biscuits. A simple salsa or hot sauce on the side adds extra flavor for those who enjoy a kick.

→ How can I reduce the fat content in this breakfast casserole?

To make a lighter version, use turkey or chicken sausage instead of pork, opt for reduced-fat cheese or use less of it, and substitute whole eggs with a mixture of whole eggs and egg whites (2 egg whites can replace 1 whole egg). Using skim or low-fat milk will also reduce the fat content while maintaining the casserole's structure and flavor.