Name: Spinach-Mushroom Brunch Casserole
Prep time: 20 min
Cook time: 40 min
Total time: 9 h
Yield: 6
Cuisine: US
Ingredients: 6 hamburger buns, preferably brioche or similar; 2 tablespoons unsalted butter, plus more for greasing; 1 cup finely chopped yellow onion; 2 cups sliced cremini mushrooms; 3 teaspoons dried Italian herb blend; 2 teaspoons garlic granules; 2 teaspoons sweet paprika; Sea salt and freshly ground black pepper, to taste; 3 cups coarsely chopped fresh spinach, baby spinach preferred; 6 slices thick-cut bacon, cooked until crisp, drained, and chopped; 1 1/2 cups shredded sharp Cheddar-Monterey Jack cheese blend, or your favorite cheese combination; 6 large eggs, lightly beaten; 2 cups whole milk

Elevate your brunch game with this effortlessly elegant casserole! Transform simple ingredients and day-old buns into a savory, make-ahead masterpiece that will impress your guests and free up your morning.

Follow The Directions

01

Step

Preheat oven to 350°F (175°C). Grease a 13x9 inch casserole dish with butter. (5 minutes)

02

Step

Place the bun tops, cut-side down, in the prepared casserole dish. Reserve the bun bottoms. (2 minutes)

03

Step

In a large skillet, melt butter over medium-high heat until shimmering. (3 minutes)

04

Step

Add chopped onion and sauté until softened, about 3-5 minutes. (5 minutes)

05

Step

Add sliced mushrooms and cook, stirring occasionally, until they release their moisture and begin to brown, about 5-7 minutes. Reduce heat to medium if needed to prevent burning. (7 minutes)

06

Step

Stir in Italian herbs, garlic granules, paprika, salt, and pepper. Add spinach and cook, stirring, until wilted, about 2-3 minutes. Remove from heat. (5 minutes)

07

Step

Spoon half of the vegetable mixture evenly over the bun tops in the casserole dish. Scatter half of the bacon and cheese evenly on top. (5 minutes)

08

Step

Place the bun bottoms, cut-side up, in the casserole dish to form the top layer. (2 minutes)

09

Step

Spoon the remaining vegetable mixture, bacon, and cheese over the top layer of buns. (5 minutes)

10

Step

In a separate bowl, whisk together eggs and milk until well combined. (3 minutes)

11

Step

Pour the egg mixture evenly over the casserole, ensuring all buns are moistened. Gently press down on each bun with a spatula to submerge them slightly in the liquid. (3 minutes)

12

Step

Cover the casserole dish tightly with plastic wrap and refrigerate for at least 8 hours, or preferably overnight. (8 hours)

13

Step

Remove the casserole from the refrigerator and let it sit at room temperature for 30 minutes to take the chill off. (30 minutes)

14

Step

Bake in the preheated oven for 35-40 minutes, or until the casserole is golden brown and set in the center. A toothpick inserted into the center should come out clean. (40 minutes)

15

Step

Let the casserole cool for a few minutes before slicing and serving warm. (5 minutes)

For a richer flavor, use Gruyere or Swiss cheese in addition to, or instead of, the Cheddar-Monterey Jack blend.
If you don't have hamburger buns, you can substitute with other types of bread, such as croissants or brioche, cut into similar-sized pieces.
Feel free to customize the vegetables according to your preference. Bell peppers, zucchini, or asparagus would be delicious additions.
For a vegetarian option, omit the bacon and add a can of drained and rinsed cannellini beans or chickpeas to the vegetable mixture.
Make sure to press down firmly on the buns to ensure they soak up the egg mixture properly. This will prevent them from drying out during baking.

RECIPE REVIEWS

Avarage Rating: 4.5/ 5 ( 13 Ratings)

Total Reviews: (8)

Yazmin Gulgowski
Jun 17, 2025
I didn't have quite enough cheese, so I added some Parmesan as well. It worked great!
Salvador Greenfelder
May 20, 2025
So easy to make and customize. I added sausage!
Jedediah Emmerich
May 17, 2025
This was a huge hit at our brunch! Everyone loved the combination of flavors and the ease of making it ahead of time.
Maximilian Kautzer
May 11, 2025
My family requests this casserole every holiday now. It's become a tradition!
Austin Schmidt
Apr 7, 2025
I added a pinch of red pepper flakes for a little extra heat. It was the perfect touch!
Micah Grant
Mar 8, 2025
Best Brunch Casserole I've ever had! Will make it again and again!
Colin Bogan
Jan 20, 2025
I found that 45 minutes was needed for the center to fully cook.
Leonard Auer
Dec 12, 2024
I substituted sourdough bread for the hamburger buns and it was amazing! Gave it a nice tang.

Spinach-Mushroom Brunch Casserole