Creamy Brussels Sprouts Casserole with Mushrooms

This Brussel Sprout Casserole is an impressive, flavor-packed side dish made with fresh Brussels sprouts and a homemade cream-of-mushroom-style sauce. It’s creamy, satisfying, vegetarian, and naturally gluten free when thickened with cornstarch instead of flour.

From-scratch but quick to assemble—this recipe takes about 15 minutes to prep and is ideal for holiday tables or a simple weeknight dinner.

With Thanksgiving approaching, this casserole is a great way to update the classic green bean casserole using fresh ingredients. Instead of canned soup, the sauce is made from sautéed mushrooms, garlic, thyme, broth and half-and-half, thickened with cornstarch for a silky, gluten-free finish.

The finished dish is rich and creamy yet still feels wholesome—perfect as a holiday side or as part of an everyday meal. It’s been a reliable favorite at gatherings, and it pairs beautifully with roasted meats, poultry, or a simply roasted vegetable main.

Ingredients

• 2 tablespoons unsalted butter
• 6 ounces baby bella (or portobello) mushrooms, diced
• 1 teaspoon kosher salt
• 1 teaspoon black pepper
• 1 teaspoon fresh thyme leaves
• 2 cloves garlic, minced
• 1/4 teaspoon ground nutmeg
• 2 tablespoons cornstarch
• 1 cup vegetable broth (or chicken/turkey broth if not vegetarian)
• 1 cup half-and-half
• 1 1/2 pounds fresh Brussels sprouts, trimmed and halved
• 1/4 cup grated Parmesan cheese (or Gruyère/sharp cheddar)

Measurements above are for about 4 servings. To scale the recipe, multiply all ingredient amounts by 2 for roughly 8 servings, or by 3 for about 12 servings.

Step-by-step instructions

1. Preheat the oven to 350°F (175°C).
2. Melt the butter in a large skillet over medium-high heat. Add the diced mushrooms, salt, pepper and thyme. Cook, stirring occasionally, for 5–6 minutes until the mushrooms release their liquid and begin to brown.
3. Add the minced garlic and nutmeg and cook 2–3 minutes more until fragrant.
4. Sprinkle the cornstarch evenly over the mushrooms, then pour in the vegetable broth while stirring to combine. Simmer for 1–2 minutes to incorporate the cornstarch.
5. Reduce heat to medium-low and stir in the half-and-half. Continue to simmer for 6–8 minutes until the sauce thickens and becomes creamy.
6. Meanwhile, trim the ends and outer leaves from the Brussels sprouts and halve or quarter them depending on size. Place the prepared sprouts in a 9 x 12-inch oven-safe baking dish.
7. Pour the creamy mushroom sauce over the sprouts and toss gently to coat. Sprinkle the grated Parmesan evenly on top.
8. Bake uncovered in the preheated oven for 40 minutes, until the sprouts are tender and the top is lightly golden.
9. Remove from the oven, let rest a few minutes, then serve warm.

Frequently asked questions

• Do I need to boil or blanch the Brussels sprouts first? No—halved sprouts cook through in the oven and develop great flavor when baked in the creamy mushroom sauce.
• How many does this serve? The recipe makes a side dish for about 4–6 people. If you’re feeding a larger group, double or triple the ingredients as needed.
• How long will leftovers keep? Stored in an airtight container, leftovers will keep in the refrigerator for up to 5 days.
• What’s the best way to reheat? Reheat in a 350°F oven covered with foil for 10–15 minutes, or microwave single portions for about 2 minutes.
• Can I make this vegan? Yes. Use a vegan cream-of-mushroom sauce (dairy-free milk and a plant-based thickener) and omit the Parmesan or use a vegan cheese alternative.

Turn it into a main dish

This casserole makes a hearty main when you add protein. Simple options:

• Chicken: Sear 1 lb cubed boneless, skinless chicken seasoned with salt, pepper and a little thyme for 4–6 minutes until mostly cooked. Add to the baking dish with the sprouts and pour the mushroom sauce over before baking.
• Bacon: Cook 4–6 slices chopped thick-cut bacon until crisp. Remove bacon, reserve the rendered fat and use it to sauté the mushrooms. Stir the cooked bacon into the casserole after baking.
• Sausage: Roast or pan-cook 3–4 sausage links, slice them and fold into the casserole after baking, or add partially cooked slices to the dish for the final bake.

What to serve it with

This casserole pairs well with a variety of mains. Some classic matches include:

• Marinated sirloin steak
• Oven-roasted turkey breast
• French onion pot roast
• Chicken stroganoff (pressure-cooker or stovetop)
• Bacon-wrapped turkey breast

More Brussels sprouts recipes

If you love Brussels sprouts, try these variations for future menus:

• Roasted Brussels sprouts with maple and apples
• Grilled Brussels sprouts
• Maple bacon Brussels sprouts
• Stuffed acorn squash with Brussels sprouts and cranberries
• Brussels sprout salad with Dijon dressing

Nutrition (approximate per serving)

• Calories: 261 kcal
• Carbohydrates: 25 g
• Protein: 11 g
• Fat: 15 g (Saturated fat: 9 g)
• Sodium: ~1034 mg
• Fiber: 7 g
• Vitamin C: ~146 mg

Notes & tips

• Cornstarch is a great gluten-free thickener—mix it into the hot pan so it disperses evenly and gives a smooth sauce.
• Swap vegetable broth for chicken or turkey broth if you’re not vegetarian.
• Gruyère or sharp cheddar work nicely instead of Parmesan for a different flavor profile.
• Leftovers reheat well; store in an airtight container for up to 5 days.
• To scale the recipe: multiply all ingredient amounts by 2 to serve about 8–12 people, or by 3 for larger gatherings.