Easy Brussels Sprouts Casserole Recipe
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Brussels Sprouts Casserole is the vegetable most people at the table expect to dislike, which makes it the one worth getting right. Roasting the sprouts first, then folding them into a simple sauce and finishing with crispy fried onions, is what turns the skeptics around.
I’ve cooked long enough as a vegetarian to know the sprouts do better roasted than boiled, and that’s the whole difference here. The browning gives them a nutty edge, and the creamy sauce and crunchy topping do the rest.
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Why You’ll Love This Recipe
- Roasting the sprouts before they go under the sauce gives them a browned, nutty flavor that boiling never will.
- The sauce is a plain butter, flour, and milk base, so there’s no special ingredient to buy and nothing tricky about it.
- It comes together in about 40 minutes from a short list of pantry staples, which makes it an easy side for a holiday plate or a Tuesday.
- You can roast the sprouts a day ahead, so the actual assembly on the day is quick.
- If you like this method, it’s the same one behind my Cheesy Cauliflower Casserole, so it’s an easy pair to learn together.
Ingredients You’ll Need
You’ll need all the ingredients shown in the photograph below.
Brussels sprouts. You’ll need 4 cups, trimmed and cut in half. Fresh is what I’d use here. Halving them matters, because the cut side is what browns against the dish and gives you that roasted flavor. Frozen sprouts hold more water and won’t brown the same way.
Butter, flour, and milk. These three make the sauce. The flour is doing the structural work here, thickening the milk into something that coats the sprouts instead of running off them. There’s no cream or cheese in the base, so it stays light enough to let the roasted sprouts lead.
Garlic powder and onion. A quarter cup of finely chopped onion and a quarter teaspoon of garlic powder season the sauce. Cooking the onion until it’s soft and translucent first takes the raw edge off.
Fried onions. These go on at the end as a topping, not into the bake. They’re the crunch, so keeping them crisp is the point.
How to Make Brussels Sprouts Casserole
A complete printable recipe and the measurements in both US customary and metric are available in the recipe card below.
Prep and Roast the Brussels Sprouts
Heat the oven to 350°F. Trim the sprouts, cut them in half, and toss them in a casserole dish with the olive oil, salt, and pepper. Roast for 20 minutes, until they start to brown. This first bake is where the flavor comes from, so let them get some color.
Make the Sauce
While the sprouts roast, melt the butter in a small saucepan over medium heat. Add the chopped onion and garlic powder and cook for 5 to 7 minutes, until the onion is soft. Stir in the flour to form a paste, then pour in the milk slowly, whisking as you go so it doesn’t go lumpy. Keep stirring until it thickens.
Combine and Bake Again
Pour the sauce evenly over the roasted sprouts and return the dish to the oven for another 10 minutes, until the top is golden and bubbling.
Garnish and Serve
Sprinkle with fresh parsley and scatter the crispy fried onions over the top just before serving, so they stay crunchy.
Garnish and Serve
When the casserole is done baking, sprinkle with fresh parsley and top with crispy fried onions before serving.
Recipe Notes and Expert Tips
- Roast in a single layer. Give the sprouts room in the dish so they roast instead of steaming. Crowded sprouts release moisture and go soft rather than browning.
- Add the milk slowly. Whisk the milk into the flour paste a little at a time. Adding it all at once is how you get lumps. If the finished sauce is too thick, loosen it with an extra splash of milk.
- Don’t overbake the second time. Pull the dish as soon as the top is golden and bubbling. Left too long, the sprouts lose their firmness, and the texture goes flat.
- Keep the fried onions for the end. Adding them before serving keeps them crisp. Baked under the sauce, they soften, and you lose the crunch that makes the dish.
Recipe Variations
- Swap the all-purpose flour for a gluten-free flour blend to make the sauce gluten-free. The recipe card notes this one, and it works as a straight one-to-one exchange.
- Stir a handful of grated cheese into the sauce before it goes over the sprouts for a richer result. I haven’t tested a specific cheese or amount here, so start small and taste as you go.
- For a deeper, sweeter background flavor, cook the sauce onion longer until it takes on some color. That’s a preference of mine, and it changes the flavor without changing anything else in the method.
How to Store Leftovers
Leftover casserole keeps in the fridge for up to 3 days in an airtight container. Reheat it in a 350°F oven until warmed through, which brings back more of the crispness than a microwave does.
For make-ahead, you can roast the sprouts a day in advance and keep them in the fridge, then make the sauce and finish the bake when you’re ready to serve. That splits the work without leaving anything sitting assembled.
This one isn’t ideal for freezing. The sprouts turn mushy once thawed, and the sauce tends to separate, so it’s best eaten within a few days.
What to Serve With Brussels Sprouts Casserole
This is a side that earns its place on a holiday plate, so I build the rest of the meal around it. It sits well next to a Nut Roast as the centerpiece, and I’ll often put out a batch of Honey Roasted Carrots alongside, since they roast the same way and you can share the oven.
More Easy Casserole Recipes for You to Try at Home
If this one wins you over, I’ve got a few more bakes worth a place on your table.
- My Creamy Broccoli Casserole leans on a cheese-cracker topping for its crunch.
- The Corn Casserole is a sweet, spoonable classic for a crowd.
- For something heartier, my Eggplant Casserole layers marinara and mozzarella into a fuller main.
- My Cheesy Scalloped Potatoes use the same kind of milk-based sauce baked until golden.
Equipment
Ingredients
- 4 cups brussels sprouts trimmed and cut in half (fresh)
- 1 tablespoon olive oil
- Salt and pepper
- 1 tablespoon butter
- ¼ cup onions finely chopped
- ¼ teaspoon garlic powder
- 2 tablespoons all-purpose flour
- 1 cup milk
Toppings:
- Fresh parsley
- Fried onions
Video
Instructions
- Preheat the oven to 180ºC (350°F).
- Trim the Brussels sprouts and cut them in half. Place them in a casserole dish, drizzle with olive oil, and season with salt and pepper. Toss everything to coat evenly. Bake in the oven for about 20 minutes, until the Brussels sprouts start to brown and soften.4 cups brussels sprouts, 1 tablespoon olive oil, Salt and pepper
- In a small saucepan, melt the butter and add the onions and garlic powder. Cook for 5-7 minutes. Add the While the Brussels sprouts are roasting, melt the butter in a small saucepan over medium heat. Add the chopped onions and garlic powder, cooking for about 5-7 minutes until the onions are softened and translucent.1 tablespoon butter, ¼ cup onions, ¼ teaspoon garlic powder
- Stir in the flour to create a paste, then slowly add the milk while stirring constantly to avoid lumps. Continue stirring until the sauce thickens.flour and mix until a thick paste is formed. Add the milk and mix until well combined, stir frequently until it thickens.2 tablespoons all-purpose flour, 1 cup milk
- Take the Brussels sprouts out of the oven and pour the sauce over them, spreading it evenly. Return the casserole to the oven and bake for an additional 10 minutes, until the top is golden and bubbly.
- Once baked, garnish the casserole with fresh parsley and crispy fried onions. Serve hot.Fresh parsley, Fried onions
Notes
Nutrition
