I’m always a sucker for a good breakfast casserole. Anything I can whip together the night before and then pop in the oven first thing in the morning and can easily feed a crowd with minimal effort on my part is a win!
I saw this recipe for a Caramelized Onion & Gruyère Strata in Bobby Flay’s cookbook and it spoke to me. But it spoke louder once I contemplated adding some bacon and mushrooms, because it just feels like bacon and mushrooms belong with caramelized onions, smokey gruyère, and spinach. But if bacon doesn’t speak to you, we can’t be friends anymore. Just kidding. But really, if you don’t eat bacon or would just rather not have it, you’re perfectly fine leaving it out here and just know that’s how Bobby did it in the first place. Either way, you’re going to win all the breakfast (brunch? Brinner?) prizes. Because this is delicious.
Ingredients Needed
This is just a preview of ingredients and method, keep scrolling for full printable recipe.
- Bacon – You’ll need cooked bacon. This Oven Baked method is my go to for easy cleanup.
- French bread – Ciabata would also work. Bread should be a day old so it can absorb all of the liquid ingredients well.
- Butter
- Canola oil
- Sweet onions – Any milder onion variety is good here. Vidalia, Walla Walla, Maui, or Texas Sweet are some varieties you commonly see at grocery stores.
- Fresh mushrooms – Cremini (Baby Bella) or white button mushrooms.
- Kosher salt and black pepper
- Fresh thyme – Dried will also work.
- Gruyère cheese – Look for gruyère with other specialty cheeses near the deli.
- Frozen, chopped spinach – You could also use fresh. Just give it a quick wilt/sauté before use.
- Eggs
- Whole milk and heavy cream – Fat content provides stability to the custard base. This recipe will still work with lower total fat content, but it may change the texture to more eggy and less smooth.
- Dijon mustard
- Freshly ground nutmeg – You’ll get the best flavor from freshly grated, especially considering a lot of us probably have ancient nutmeg in our cupboards, but feel free to use ground nutmeg if that’s what you have available!
- Sautéed cherry tomatoes
- olive oil
- cherry tomatoes
- kosher salt and black pepper
- fresh chives
How to Make a Caramelized Onion & Gruyère Strata
- First we’ll caramelize some sweet onions in butter. Then we’ll add some mushrooms and cook until tender.
- Next we’ll help the cubed bread dry out and toast a little with a quick visit to the oven.
- When that’s toasted, transfer to a buttered baking dish, top with the shredded gruyère cheese, and then the mushroom and onion mix and some drained frozen spinach.
- Next we’ll mix up the custard base: eggs, milk, heavy cream, mustard, salt, pepper, and nutmeg. Pour that over the ingredients in the pan. Cover tightly and place the pan in the refrigerator for up to 24 hours (overnight is perfect if making this for breakfast or brunch).
- The next day, uncover the baking dish and bake until the top is golden and the strata doesn’t jiggle when you shake the pan. Add a little extra cheese to the top in the last 10 minutes of baking.
- Allow the strata to rest for a few minutes before serving.
- To make the cherry tomatoes, heat some olive oil in a a large sauté pan over medium heat. When hot, add cherry tomatoes, season with salt and pepper, and cook until the tomatoes begin to soften. Remove from heat and stir in chopped chives.
- To serve, use a spatula or serving spoon to dish up the strata and then top with sautéed tomatoes.
Storing and Other Tips
- Store cooled leftovers in an airtight container or tightly wrapped in the fridge and enjoy within 3-4 days for best results.
- Freeze individual portions, tightly wrapped in plastic and then foil, for up to 1-2 months. Reheat from thawed for best results.
- This dish was originally vegetarian and can easily be made without bacon. Also, if you cook your bacon in the oven, reserve about 1 tablespoon of the drippings from the pan and use the same pan to toast your bread–you won’t be sorry!
Frequently Asked Questions
Can I make this ahead of time?
This is a great make-ahead dish! Assemble the casserole up to 24 hours in advance and then bake fresh for serving.
Do I have to use gruyère?
Nope. Good substitutes include Swiss, Fontina, Emmental, or even sharp white cheddar.
Do I have to let it sit for a full 24 hours?
Not necessarily. We just want to make sure the bread gets a chance to fully soak up the custard. If you’re short on time, even a couple of hours is ok. I’d say 8-12 is better, and 24 is the max.
Caramelized Onion & Gruyère Strata
An elegant and delicious make-ahead meal, perfect for breakfast, brunch, or dinner!
Servings people (one 9×13″ pan)
Ingredients
Strata
- 12 ounces bacon cooked and chopped (option)
- 6 cups day-old French bread or ciabatta cubes
- 2 tablespoons butter plus more for the baking dish
- 1 tablespoon canola oil
- 2 large sweet onions halved and sliced
- 1 cup chopped fresh mushrooms I like baby portobellos
- kosher salt and freshly ground black pepper
- 1 tablespoon fresh thyme or 1 teaspoon dried thyme
- 2 cups grated gruyère cheese divided
- 1 10- ounce package frozen chopped spinach thawed and squeezed dry
- 10 large eggs
- 3 cups whole milk
- 1 cup heavy cream
- 2 teaspoons Dijon mustard
- ⅛ teaspoon freshly ground nutmeg
SAUTÉED CHERRY TOMATOES
- 3 tablespoons olive oil
- 2 pints cherry tomatoes
- kosher salt and freshly ground black pepper
- 3 tablespoons finely sliced fresh chives
Instructions
- If using bacon, cook bacon and drain and chop. Set aside. Butter a 9×13″ baking dish and set aside.
- Combine the butter and oil in a large sauté pan over medium heat. When hot, add the onions and toss to coat in the butter. Season with kosher salt and freshly ground black pepper. Cook the onion, stirring occasionally, until the onions are golden brown and caramelized. When the onions are nearly done cooking, add the mushrooms and cook until the mushrooms are tender and the onions are done. Remove from heat.
- Preheat oven to 325℉. Spread bread onto the baking sheet and bake for 10 minutes, stirring once halfway through. When lightly toasted, spread the bread into the prepared baking dish. Sprinkle with bacon, then add the mushrooms and onion mixture the drained spinach, and 1 ½ cups of the shredded cheese and toss to evenly distribute the ingredients.
- In a large bowl, whisk together the eggs, milk, cream, mustard, ½ teaspoon kosher salt, ¼ teaspoon freshly ground black pepper, and nutmeg. Pour the mixture evenly over the bread mixture. Cover the baking dish and refrigerate for 2-24 hours.
- When ready to bake, preheat oven to 350℉. Uncover the baking dish and bake until the mixture has puffed up and the top is golden and the strata doesn't jiggle when you shake it (about 1 hour). During the last 10 minutes of baking, add the reserved 1/2 cup of cheese. When done, remove from the oven and allow to stand for 10 minutes before serving. Use a spatula or serving spoon to dish out the casserole and then top with the sautéed cherry tomatoes.
- To prepare the cherry tomatoes, heat the oil in a large sauté pan over medium heat. When hot, add the tomatoes, season with salt and pepper, and cook until the tomatoes begin to soften (about 5-7 minutes). Remove from heat and stir in the chives. Serve on top of the strata (or alongside your favorite breakfast foods).
Notes
- This dish was originally vegetarian and can easily be made without bacon. Also, if you cook your bacon in the oven, reserve about 1 tablespoon of the drippings from the pan and use the same pan to toast your bread–you won’t be sorry!
- Store cooled leftovers in an airtight container or tightly wrapped in the fridge and enjoy within 3-4 days for best results.
- Freeze individual portions, tightly wrapped in plastic and then foil, for up to 1-2 months. Reheat from thawed for best results.
Nutrition
Calories: 631kcal, Carbohydrates: 26g, Protein: 33g, Fat: 44g, Saturated Fat: 20g, Polyunsaturated Fat: 5g, Monounsaturated Fat: 17g, Trans Fat: 0.2g, Cholesterol: 268mg, Sodium: 1046mg, Potassium: 842mg, Fiber: 3g, Sugar: 11g, Vitamin A: 5232IU, Vitamin C: 28mg, Calcium: 481mg, Iron: 4mg
Calories: 631kcal
Cost: $18
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Questions & Reviews
This looks fabulous and I can’t wait to try it this weekend. (Just a FYI, step 3 confused me and I had to read it a handful of times before I understood that the oven is only on to toast the bread, and not everything else listed on that step.)
…oh my…
Decided to make this in lieu of my usual breakfast casserole and I’m glad I did! I think I’ve found my new Christmas morning breakfast, and the fact that it’s a make-ahead is an added bonus. I did substitute shredded gouda for the gruyere (what I had on hand), but it was still delicious. Thanks for another fabulous recipe! Merry Christmas!
Looks like we are making this for Christmas morning. Thanks for a fancy breakfast dish I can make the night before. 🙂
This looks amazing! I need these in my life now!
I went to your site this morning fully expecting the post to be a message about how you are taking the week off to be with your families. You should TOTALLY do that, but I’m so happy you posted this recipe first. It sounds amazing. My kids might prefer generic crunch berries, but I’m pretty sure my husband and I will hear angels singing when we bite into it on Christmas morning.
I made it for this morning and everyone that tried it loved it. Delicious!