Broccoli Cheese Casserole with Crispy Onions

Looking for a clean and classic broccoli and cheese casserole? This recipe for broccoli casserole with crispy onions is the perfect dish! Packed with fresh broccoli plus mushrooms, each bite offers a slight crunch, complemented by a light, creamy sauce with just the right amount of cheese. Topped with crispy onions for added flavor and texture, it makes a delicious side for any meal.

As a mom and home cook (in addition to being a food blogger), I cook a lot and am always on the lookout for recipes that showcase the ingredients I am using. Unfortunately, I am often disappointed.

One of my biggest frustrations is finding recipes that feature the ingredients I am cooking with but are overloaded with sauces or cream that completely undermine the true essence and flavor of the hero ingredients.

Enter this healthy broccoli casserole featuring steamed broccoli and shiitake mushrooms. Lightly doused with a gruyere cheese sauce, and baked to bubbling perfection, the vegetables really shine. Topped with crispy fried onions, for the ultimate crunch, I’m sure once you taste this casserole you’ll agree it will make a great side dish for the holidays or any meal any time of the year. It also happens to be pure comfort food which is great for those fall and winter days.

Broccoli, onions, shiitake mushrooms, gruyere cheese, flour, butter, salt and pepper, crispy onions and milk with a plaid dish towel.

What you’ll need

Before we get to the ingredients you’ll need to make my broccoli bake recipe, Let me tell you what you won’t find in this recipe. You won’t find unnecessary sauces, no cream of mushroom soup, no mayonnaise and not a lot of cheese!

Broccoli crown: I just used the crowns from the broccoli and removed stems. Keep the stems for a stir fry or soup.
Shiitake mushrooms: Mini shiitakes add a load of umami taste. If using larger mushrooms be sure to slice in half.
Butter: I like simmering the aromatics in butter for a rich flavor though olive oil also works.
Aromatics: I used a combination of a small diced onion and minced garlic.
All-purpose flour: A touch of flour helps create a roux to thicken the sauce of the casserole. Use gluten-free flour if you want a gluten-free casserole.
Milk: Use your preferred milk, plant-based milk works well too. If you use plant-based make sure it is unsweetened.
Gruyère cheese: Shredded gruyère adds a unique cheesy flavor. See note below about substituting with parmesan cheese.
Crispy onions: You can pick up a can of crispy onions at the grocery store. Look for gluten-free onions for a gluten-free broccoli casserole.

Garlic and onion sauteed in a cast iron pan with butter, plaid dish towel with onion and rosemary, crispy onions.

Adding flour to the aromatics and whisk to combine, onion, rosemary, and a plaid dish towel, crispy onions.

Broccoli and mushrooms in a steamer basket, onions, rosemary and plaid dish towel.

How To Make Broccoli Casserole

Steam broccoli and shiitake mushrooms until fork tender but not too soft.
Melt butter in a large skillet and sauté onion and garlic until fragrant and golden brown.
Stir in the flour and as it thickens pour in the milk slowly, stirring well using a rubber whisk. Season with salt and pepper.
Stir in the gruyère cheese, mix to combine then remove from stove.
Transfer broccoli and mushrooms to a baking dish, pour the creamy cheese sauce over and toss to coat.
Sprinkle the casserole with as many of the crispy onions as you like, cover with foil, and bake until hot and bubbling.

Broccoli and baby shiitake mushrooms in a casserole, crispy onions, plaid dish towel.

RECIPE TIPS

✅ Don’t overcook the sauce, it will thicken quickly. You can always adjust the thickness by adding more milk.

✅ Remove the foil about 5 minutes before the casserole is done to crisp up the onions.

✅ Watch the broccoli and mushrooms well so they don’t overcook as they will continue to cook in the casserole and you don’t want them to get too soft.

✅ If you find the casserole sauce is too thick after it’s been refrigerated as it will thicken over time, pour more milk over it.

Broccoli and baby shiitake mushrooms with cream sauce poured over, crispy onions, and a plaid dish towel.

FAQs

can i use frozen broccoli to make this casserole?

Yes, if you can’t find any fresh broccoli, frozen is a good substitute.

Can I use Cream of mushroom soup?

As much as I encourage you to try making this easy creamy cheese sauce, if you are pressed on time you can use cream of mushroom soup.

does this broccoli casserole with cheese freeze well?

Yes! see notes below on storage and freezing instructions.

can I prepare this the day before and bake the day of?

Absolutely! Once you have built your casserole cover with foil and refrigerate until ready to bake.

Broccoli and mushroom casserole with crispy onions, plaid dish towel, and rosemary.

Storage and Make Ahead

Storage: This crispy, cheesy broccoli and mushroom casserole will keep well in an airtight container in the fridge for up to 4 days. Alternatively, cover tightly with plastic wrap or aluminum foil. Reheat in the oven so the onions get crisp again.

Freezer: Freeze uneaten leftovers for up to 3 months. Thaw in the fridge overnight. Note, your broccoli may be a little softer once it’s been frozen and thawed.

Make Ahead: This casserole is perfect to have on hand for busy weekdays. Prepare during your meal prep and stash it in the fridge for a few days. Everyone can easily help themselves to a serving for a snack, lunch, dinner, or even breakfast.

Broccoli and mushroom casserole with crispy onions, rosemary.

Looking for more quick and easy casseroles?

Place clean broccoli and shiitake mushrooms in a steamer basket and steam for about 8-10 minutes until fork tender but not too soft.
Meanwhile, melt butter in a large skillet. Sauté onion and garlic until fragrant and golden brown.
Stir in the flour. It will quickly thicken so have the milk ready. Once the flour has incorporated into the butter and onion mix, stir in the milk slowly, stirring well using a rubber whisk. Season well with salt and pepper. (See notes)
Next add the gruyère cheese. Stir well to combine then remove from stove (about 2 minutes). Don’t overcook the sauce, it will thicken quickly. You can always adjust thickness with more milk
Transfer broccoli and mushrooms to a baking dish.
Pour creamy cheesy sauce over the veggies, then toss to coat evenly.
Top with crispy onion. As much or as little as you like. Cover with foil.
Bake at 375F degrees for about 25 minutes. Feel free to remove the foil about 5 minutes before it is done to crisp up the onions.

A great substitute for gruyère cheese in this recipe is parmesan cheese or you can use a combination of both.
If you opt to use parmesan cheese, know that the recipe will require less added salt since the parmesan cheese is salty