Creamy Parmesan Brussels Sprouts Casserole

The smell of butter hitting a hot skillet on a cold November evening is enough to make anyone forget whatever bad mood they were carrying into the kitchen. I threw this casserole together on a whim before a Friendsgiving where I had volunteered to bring a side and promptly forgot until two hours before. Now it is the one dish people text me about every single holiday season, asking if I am bringing the sprouts.

My friend Dave stood in my kitchen eating it straight from the baking dish with a serving spoon before I could even transfer it to a serving bowl. He looked guilty for about half a second and then kept going.

Ingredients

• 1 ½ lbs (680 g) Brussels sprouts, trimmed and halved: Pick ones that are tight, bright green, and on the smaller side because they tend to be sweeter and cook more evenly.
• 1 medium onion, finely chopped: A yellow onion works best here since it adds sweetness without sharpness.
• 3 cloves garlic, minced: Fresh garlic matters in this recipe because the sauce is simple and every ingredient shows.
• 1 ½ cups (360 ml) heavy cream: Do not try to substitute half and half because the sauce needs the fat to thicken properly and coat the sprouts.
• ¾ cup (75 g) grated Parmesan cheese: Grate it yourself from a block for the best melting behavior.
• 1 cup (100 g) shredded mozzarella cheese: This adds stretch and mellow creaminess that balances the salty bite of Parmesan.
• 2 tbsp (28 g) unsalted butter: This is the foundation of your flavor base so use real butter.
• 1 tsp salt: Kosher salt gives you the best control over seasoning.
• ½ tsp black pepper: Freshly cracked is always worth the extra few seconds.
• ½ tsp dried thyme: Rub it between your fingers before adding to wake up the oils.
• ¼ tsp ground nutmeg: This tiny amount is the secret that makes the whole sauce taste richer and more complex.
• ½ cup (50 g) panko breadcrumbs: Panko stays crunchier than regular breadcrumbs after baking.
• ¼ cup (25 g) grated Parmesan cheese for topping: This melts into the panko and creates little golden crispy bits.
• 1 tbsp (15 ml) olive oil: Tossing the panko with oil ensures even browning across the whole top.

Instructions

Get your oven ready:

Preheat to 400°F (200°C) and lightly grease a 9x13 inch baking dish so nothing sticks later when you are trying to serve.

Blanch the sprouts:

Dump the halved Brussels sprouts into a large pot of salted boiling water for 3 to 4 minutes until they are just tender when pierced with a fork. Drain them really well because excess water will make your sauce watery and sad.

Build the flavor base:

Melt the butter in a large skillet over medium heat and sauté the onion for 3 to 4 minutes until it goes translucent and soft. Add the garlic and stir for one more minute until your kitchen smells incredible.

Make it creamy:

Pour in the heavy cream and bring it to a gentle simmer without letting it boil. Stir in the Parmesan, mozzarella, salt, pepper, thyme, and nutmeg, and keep stirring for 2 to 3 minutes until the cheese melts and the sauce thickens slightly.

Combine and assemble:

Fold the blanched sprouts into the sauce until every single one is coated, then spread the mixture evenly into your prepared baking dish.

Whip up the topping:

In a small bowl, toss the panko with the remaining Parmesan and olive oil until the crumbs are evenly moistened, then scatter it all over the top of the casserole.

Bake until golden:

Slide it into the oven for 20 to 25 minutes until the edges are bubbling and the top is a deep golden brown. Let it rest for a few minutes before serving so the sauce settles.

Pin It

The year my oven broke halfway through baking this casserole, I finished it under the broiler in five minute increments and the topping was actually the best it has ever been. Sometimes kitchen disasters have a silver lining.

Swaps and Additions That Work

Stir in a handful of cooked chopped bacon or crispy pancetta right before assembling if you want to take this into non vegetarian territory. Gruyère or Swiss cheese can replace the mozzarella for a deeper, nuttier flavor that feels a little more grown up.

What to Serve It With

This casserole sits happily next to roast turkey, baked ham, or a simple roast chicken dinner. For a vegetarian meal, pair it with a bright lemony salad and some crusty bread to soak up the extra sauce.

Storage and Reheating

Cover leftovers tightly and keep them in the fridge for up to three days. Reheat in a 350°F oven for about 15 minutes to bring the crisp back on top.

• You can assemble the whole thing a day ahead and bake it right before serving.
• The topping will lose its crunch in the fridge so add it fresh if you are making it ahead.
• Let it sit at room temperature for about twenty minutes before baking if it has been in the fridge overnight.

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This is the kind of dish that turns a regular Tuesday dinner into something that feels like a celebration. Make it once and it will follow you for years.

Recipe FAQs

→ Can I prep this ahead of time?

Yes. Assemble the casserole up to the panko topping, cover and refrigerate for 24 hours. Add the topping and bake 20–25 minutes until heated through and golden.

→ How should I blanch the Brussels sprouts?

Boil salted water and add halved sprouts for 3–4 minutes until just tender. Drain well and pat dry to avoid a watery sauce before combining.

→ What cheese substitutions work well?

Gruyère or Swiss can replace mozzarella for a nuttier profile. Increase Parmesan slightly if you prefer a sharper finish.

→ How can I make it crispier on top?

Toss panko with olive oil or melted butter before sprinkling, and broil for 1–2 minutes at the end to achieve extra browning—watch closely to prevent burning.

→ Is there a way to reduce richness?

Use half-and-half or a mix of milk and cream instead of heavy cream, and trim back the butter slightly. A squeeze of lemon brightens the flavors.

→ How should leftovers be stored and reheated?

Cool completely, cover and refrigerate up to 3 days. Reheat in a 350°F (175°C) oven until warmed through to preserve texture; avoid microwaving for best results.