Imagine cutting into a golden, puffy casserole to reveal layers of crusty bread soaked in a rich custard, studded with vibrant spinach and pockets of nutty, melted Gruyère cheese. This Spinach and Gruyère Breakfast Casserole is the kind of dish that makes weekend mornings special and turns ordinary brunches into memorable occasions. It’s essentially a savory bread pudding that’s both elegant and incredibly satisfying, with the sophisticated flavor of Gruyère cheese elevating it far above standard breakfast fare. The beauty of this casserole lies not just in its delicious taste, but in its convenience. You assemble it the night before, let it rest in the refrigerator while the bread soaks up all that creamy egg mixture, then simply pop it in the oven in the morning. Your kitchen will fill with the most amazing aroma while you relax with coffee, and you’ll serve something that looks and tastes like you worked much harder than you actually did. Perfect for holidays, houseguests, or any time you want breakfast to feel like an event.
Serving Quantity: 8 servings
Cooking Time: 50 minutes (plus overnight refrigeration and 10 minutes prep time)
Nutrition Information (per serving):
- Calories: 420
- Protein: 22g
- Fat: 24g
- Carbohydrates: 28g
- Fiber: 2g
- Sugar: 5g
- Sodium: 720mg
1. Gather Your Ingredients
For the casserole:
- One pound day-old French bread or sourdough, cut into 1-inch cubes (about 8 cups)
- Two tablespoons unsalted butter
- One medium yellow onion, diced
- Three garlic cloves, minced
- Five ounces fresh baby spinach (about 5 cups packed)
- Eight large eggs
- Two and a half cups whole milk
- One cup heavy cream
- Two cups Gruyère cheese, shredded (about 8 ounces)
- Half cup grated Parmesan cheese
- One tablespoon Dijon mustard
- One teaspoon salt
- Half teaspoon black pepper
- Quarter teaspoon ground nutmeg
- Quarter teaspoon cayenne pepper (optional)
- Two tablespoons fresh chives, chopped
- One tablespoon fresh thyme leaves (or one teaspoon dried)
For topping:
- Half cup Gruyère cheese, shredded
- Two tablespoons unsalted butter, cut into small pieces
2. Prepare the Bread
If your bread is fresh rather than day-old, cut it into one-inch cubes and spread the cubes on a large baking sheet. Place in a 300-degree oven for about 10 to 15 minutes to dry them out slightly. Day-old or slightly stale bread is ideal because it absorbs the custard without becoming too soggy. Fresh bread can work but may result in a mushier texture. You want the bread to be able to soak up liquid while maintaining some structure. Once your bread cubes are ready, place them in a very large bowl and set aside.
3. Sauté the Aromatics
In a large skillet, melt two tablespoons of butter over medium heat. Add the diced onion and cook for about 5 to 6 minutes, stirring occasionally, until softened and translucent. The onion should be tender and starting to turn golden at the edges. Add the minced garlic and cook for another minute, stirring constantly, until fragrant. Be careful not to burn the garlic as it will become bitter. The cooked onion and garlic provide an aromatic foundation that infuses the entire casserole with savory depth.
4. Wilt the Spinach
Add all five ounces of fresh spinach to the skillet with the onion and garlic. It will seem like an enormous amount at first, but spinach wilts down dramatically. Toss the spinach with tongs or a spatula for about 2 to 3 minutes until it’s completely wilted and reduced in volume. Season with a pinch of salt and pepper. Transfer the spinach mixture to a colander and press down firmly with the back of a spoon to squeeze out as much excess liquid as possible. This step is crucial because excess moisture will make your casserole watery. Let the spinach cool slightly, then roughly chop it. Add the cooled spinach mixture to the bowl with the bread cubes.
5. Prepare the Custard Base
In a large mixing bowl, whisk together eight eggs until well beaten with no streaks of white or yolk visible. Add the milk, heavy cream, Dijon mustard, salt, black pepper, nutmeg, and cayenne pepper if using. Whisk vigorously for about 1 minute until everything is completely combined and slightly frothy. The nutmeg adds a subtle warmth that’s traditional in savory custards, while the Dijon provides a slight tang and helps emulsify the mixture. The combination of milk and cream creates the perfect balance of richness without being too heavy.
6. Combine Everything
Add one and a half cups of the shredded Gruyère cheese, the grated Parmesan, chopped chives, and thyme to the bowl with the bread and spinach. Toss everything together gently with your hands or a large spoon until well distributed. Pour the custard mixture over the bread mixture. Use your hands or a large spoon to press down on the bread cubes, making sure every piece gets submerged in the liquid and has a chance to soak. Let the mixture sit for about 5 minutes, then press down again. The bread should be saturated but not completely falling apart.
7. Assemble in the Baking Dish
Generously butter a 9-by-13-inch baking dish or spray it with non-stick cooking spray. Pour the entire bread and custard mixture into the prepared dish, spreading it evenly and pressing down gently so everything is compact and level. Make sure the cheese and spinach are distributed evenly throughout rather than all settling to the bottom. The mixture should come nearly to the top of the dish. Sprinkle the remaining half cup of Gruyère cheese evenly over the top. Dot the surface with small pieces of butter, which will help create a golden, crispy top as it bakes.
8. Refrigerate Overnight
Cover the baking dish tightly with plastic wrap or aluminum foil. Place it in the refrigerator and let it rest for at least 8 hours, or preferably overnight. This resting time is not optional. It allows the bread to fully absorb the custard, ensures even distribution of flavors, and results in a casserole that’s creamy on the inside with distinct layers rather than a scrambled mess. The overnight rest also allows you to do all the work the day before, making morning cooking completely stress-free. You can prepare this up to 24 hours in advance.
9. Bake to Golden Perfection
When ready to bake, remove the casserole from the refrigerator and let it sit at room temperature for about 30 minutes while you preheat the oven. This takes the chill off and ensures more even baking. Preheat your oven to 350 degrees Fahrenheit. Remove the covering from the casserole. Bake uncovered for 45 to 50 minutes until the casserole is puffed and golden brown on top, the edges are crispy, and a knife inserted in the center comes out mostly clean with just a bit of creamy custard clinging to it. The center should be set but still slightly jiggly when you gently shake the pan. If the top browns too quickly before the center is set, tent it loosely with aluminum foil for the remaining baking time.
10. Rest and Serve
Remove the casserole from the oven and let it rest for 10 to 15 minutes before serving. This resting period allows the custard to set fully, making it much easier to cut clean squares and preventing it from being too liquidy when served. The casserole will deflate slightly as it cools, which is completely normal. Cut into eight equal portions using a sharp knife or pie server. Use a spatula to lift each piece out carefully, making sure to get all the layers. Serve warm with optional accompaniments like fresh fruit, crispy bacon, breakfast sausage, or a simple mixed greens salad for a complete brunch spread.
Tips for Perfect Results
- Day-old bread is essential for the best texture. Fresh bread becomes too soggy while very stale bread won’t absorb enough custard. If your bread is fresh, dry it out slightly in a low oven first.
- Don’t skip squeezing the excess liquid from the spinach. Watery spinach is one of the main causes of a soggy, unappetizing casserole.
- Gruyère cheese is worth the splurge for its nutty, complex flavor that melts beautifully. Swiss cheese is an acceptable substitute, but avoid pre-shredded cheese which contains anti-caking agents that affect melting.
- The overnight refrigeration is crucial for proper texture. If you’re truly in a rush, let it sit for at least 2 hours, but overnight is always better.
- Bring the casserole to room temperature before baking. Putting a cold casserole straight into the oven results in uneven cooking with cold spots in the center.
- The casserole is done when it’s puffed, golden, and set in the center but still has a slight jiggle. Overbaking results in a dry, rubbery texture.
- For individual portions perfect for meal prep, divide the mixture among greased muffin tins and bake for 25 to 30 minutes. These freeze beautifully.
- Add cooked, crumbled bacon or diced ham to the bread mixture for extra protein and a heartier casserole that can stand alone as a complete meal.
- Substitute other greens like kale, chard, or a combination. Just make sure to cook them until tender and squeeze out excess moisture.
- Leftovers can be stored covered in the refrigerator for up to 4 days. Reheat individual portions in the microwave for 1 to 2 minutes or cover the entire dish with foil and reheat in a 325-degree oven for 20 minutes. The casserole loses some of its puffiness when reheated but still tastes delicious.
