If you love Brussels sprouts but want to elevate them to something a little extra, this Cheesy Brussels Sprout Casserole is your answer. Tender Brussels sprouts are smothered in a creamy, cheesy sauce like in my Brussels Sprouts Gratin (which you will also want to make). Then, I topped it with golden, crispy onions for a side dish that feels indulgent yet approachable. It’s perfect for Sunday roasts, or any weeknight when you want vegetables that everyone will actually reach for.
Ingredients & Substitutions
- Brussels Sprouts: Use 2 pounds of fresh Brussels sprouts, washed, trimmed, and halved. Choosing firm, bright green sprouts ensures they stay tender but not mushy. You can also use frozen Brussels sprouts; just thaw and pat dry before cooking.
- Butter: Unsalted butter adds richness and depth to the sauce. If you only have salted butter, reduce the added salt slightly.
- Onion & Garlic: A finely diced yellow onion softens beautifully in the butter and provides subtle sweetness, while minced garlic adds savory depth. For a milder flavor, reduce the garlic to 1 teaspoon.
- Crushed Red Pepper Flakes: Just ½ teaspoon gives a gentle hint of heat without overpowering the dish. You can leave them out for a mild casserole.
- Flour: Helps thicken the sauce. All-purpose flour works best, but a gluten-free flour blend can be used if needed.
- Chicken Broth & Heavy Cream: The combination makes a silky, flavorful sauce. For a vegetarian version, swap chicken broth for vegetable broth.
- Cheese: Gruyère adds nutty, melty richness, while Parmesan brings sharp, savory notes. You can substitute Gruyère with Fontina or Emmental if desired. For a lighter version, reduce the cheese slightly, though it will be less indulgent.
- Crispy Onions: French’s crispy fried onions are classic, but homemade versions work beautifully too, like in my Crispy Onion Scalloped Potatoes. Add them right before the last few minutes of baking for the best crunch.
- Parsley: Freshly chopped parsley is optional but adds a pop of color and freshness before serving.
FAQs
Can I make this casserole ahead of time?
Yes! Assemble everything in the baking dish, cover tightly with foil, and refrigerate for up to 24 hours.
Can I make it vegetarian?
Absolutely! Swap the chicken broth for vegetable broth, and the dish will still be creamy, cheesy, and flavorful.
Can I adjust the heat level?
Yes! The 1/2 teaspoon of crushed red pepper flakes adds a gentle hint of heat. Omit them entirely for a completely mild casserole. Or, add extra for even more of a kick!
Are there variations or add-ins I can try?
Definitely! You can:
- Add bacon or pancetta for a smoky, savory touch.
- Mix in sautéed mushrooms or roasted shallots.
- Sprinkle toasted nuts like almonds or pecans over the top for crunch and flavor.
- Fold in a handful of fresh herbs like thyme or rosemary.
How To Store Cheesy Brussels Sprout Casserole
Room Temperature: Serve immediately for the best flavor and texture. The creamy sauce and crispy onions are at their peak right out of the oven.
Refrigerator: Store leftovers in an airtight container for up to 3 days. To reheat, transfer to an oven-safe dish and warm at 350°F for 10-15 minutes, or microwave in portions until heated through. If the onions have softened, you can sprinkle a few extra crispy onions on top before reheating to restore crunch.
Freeze Before Baking: Assemble the casserole (without fried onions) in a freezer-safe dish. Cover tightly with foil and freeze for up to 2 months. When ready to bake, thaw in the refrigerator overnight, then bake as directed. Add fresh crispy onions during the final 5 minutes of baking.
Freeze After Baking: It’s best to freeze only if absolutely necessary, and again, leave the crispy onions off. Cool the casserole completely, cover tightly, and freeze for up to 2 months. Reheat in the oven at 350°F until warmed through, then add fresh crispy onions for topping.
Cheesy Brussels Sprout Casserole
Ingredients
- 2 pounds Brussels sprouts, washed, trimmed, and halved
- ¼ cup (½ stick / 57 g) unsalted butter
- 1 medium yellow onion, finely diced (about 1 cup)
- 4 teaspoons garlic, minced
- ½ teaspoon crushed red pepper flakes
- ¼ cup (31 g) all-purpose flour
- 1 cup (252 g) chicken broth
- 1 cup (238 g) heavy whipping cream
- 1 teaspoon kosher salt
- ½ teaspoon black pepper
- 1 cup (113 g) Gruyère cheese, shredded
- 1 cup (100 g) Parmesan cheese, freshly grated
- 1 ½ cups (100 g) French’s crispy fried onions, or homemade
- Fresh parsley, chopped, for garnish
Instructions
- Preheat oven to 400°F (200°C). Lightly spray a 9×13-inch baking dish with nonstick cooking spray and set aside.
- Bring a large pot of salted water to a boil. Add Brussels sprouts and cook until just fork-tender, about 4 to 5 minutes. Drain well and set aside.
- In a large skillet over medium heat, melt butter. Add diced onion and cook until softened, about 3 to 4 minutes.
- Stir in the garlic and crushed red pepper flakes, stirring constantly for 30 seconds.
- Sprinkle flour over the onion mixture and stir constantly for 1 minute to create a roux.
- Slowly whisk in the chicken broth. Continue whisking until the sauce begins to thicken slightly, about 1 to 2 minutes.
- Pour in the heavy cream and continue to whisk until the mixture is smooth, creamy, and thick enough to coat the back of a spoon, about 2 to 3 minutes.
- Season the sauce with salt and pepper.
- Add the cooked Brussels sprouts to the skillet and gently fold them into the sauce, making sure they are evenly coated.
- Transfer the Brussels sprout mixture to the prepared 9×13-inch baking dish, spreading it out evenly.
- Sprinkle the Gruyère and Parmesan cheese evenly over the top.
- Bake uncovered for 20 minutes.
- Remove from oven and immediately sprinkle French’s crispy fried onions evenly over the top.
- Return to the oven to bake for 5 more minutes.
- Let the casserole sit for 5 minutes before garnishing with chopped parsley. Serve warm.
Did you make this recipe?
You can tag me at @iamhomesteader.
What the Test Kitchen had to say about this recipe:
Autumn
These are really good! I love the crunch from the fried onions to go with the cheesy Brussels sprouts.
Elizabeth
I loved this! I want to serve this instead of (or alongside) green bean casserole at Thanksgiving!
Stephanie
This is creamy, cheesy, and perfectly crispy on top.
Bella
I liked it, and then I added some crispy bacon pieces to my dish, and I made it even better! So, I highly recommend the bacon!
