Creamy Parmesan Brussels Sprouts Casserole

The smell of butter hitting a hot skillet on a cold November evening is enough to make anyone forget their bad mood, and that is exactly how this Brussels sprouts casserole came into my life, born out of stubbornness and a refrigerator that needed clearing out before a holiday trip.

My sister once declared she would never eat Brussels sprouts, then went back for a third helping of this casserole at Thanksgiving and refused to admit she had changed her mind.

Ingredients

• 1 1/2 lbs (680 g) Brussels sprouts, trimmed and halved: Fresher sprouts are tighter and sweeter, so pick ones that feel heavy and look bright green with no yellowing leaves.
• 1 medium onion, finely chopped: Yellow onion adds a mellow sweetness that anchors the whole sauce together.
• 3 cloves garlic, minced: Fresh garlic makes a noticeable difference here, so skip the jarred version if you can.
• 1 1/2 cups (360 ml) heavy cream: This is the luxurious base that turns humble vegetables into something worth celebrating.
• 3/4 cup (75 g) grated Parmesan cheese: Use a block and grate it yourself because pre grated Parmesan contains anti caking agents that make the sauce grainy.
• 1 cup (100 g) shredded mozzarella cheese: Mozzarella adds stretch and a gentle milky flavor that balances the sharpness of the Parmesan.
• 2 tbsp (28 g) unsalted butter: Butter gives the onions a rich head start and coats everything in warmth.
• 1 tsp salt: Seasoning in layers is the trick, so start here and adjust at the end.
• 1/2 tsp black pepper: Freshly cracked pepper brings a subtle heat that cuts through the richness.
• 1/2 tsp dried thyme: Thyme and cream are old friends, and that herbal note keeps the dish from feeling too heavy.
• 1/4 tsp ground nutmeg: A tiny amount of nutmeg is the quiet secret that makes any cream sauce taste like it came from a restaurant.
• 1/2 cup (50 g) panko breadcrumbs: Panko stays light and shatteringly crisp compared to regular breadcrumbs.
• 1/4 cup (25 g) grated Parmesan cheese (for topping): Mixing Parmesan into the topping creates those irresistible golden cheese bits on top.
• 1 tbsp (15 ml) olive oil: The oil helps the panko brown evenly without burning.

Instructions

Preheat and prepare the baking dish:

Set your oven to 400 degrees F (200 degrees C) and lightly grease a 9 by 13 inch baking dish so nothing sticks later.

Blanch the Brussels sprouts:

Drop the halved sprouts into a large pot of salted boiling water for 3 to 4 minutes until they are just tender when pierced with a fork, then drain them thoroughly because excess water will make your sauce soupy.

Build the flavor base:

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

Create the creamy sauce:

Pour in the heavy cream and bring it to a gentle simmer, then add the Parmesan, mozzarella, salt, pepper, thyme, and nutmeg, stirring constantly for 2 to 3 minutes until the cheeses melt into a silky, thickened sauce that coats the back of a spoon.

Combine and transfer:

Toss the drained Brussels sprouts with the creamy sauce until every piece is coated, then spread the mixture evenly into your prepared baking dish, making sure the sprouts sit in a single even layer.

Make the crunchy topping:

In a small bowl, stir together the panko breadcrumbs, the remaining Parmesan, and olive oil until the crumbs are evenly moistened, then sprinkle this mixture generously over the entire surface of the casserole.

Bake until golden:

Slide the dish into the oven and bake for 20 to 25 minutes until the edges are bubbling and the top is a deep golden brown, then let it rest for a few minutes before serving so the sauce has time to settle.

Save

The first time I served this at a potluck, a stranger tracked me down to ask for the recipe, and we ended up talking about our grandmothers for an hour.

Serving Suggestions

This casserole holds its own next to roasted chicken or turkey, but I have also eaten it over a bed of arugula with a squeeze of lemon for a lazy weeknight dinner that felt surprisingly elegant.

Making It Your Own

Stir in cooked chopped bacon or pancetta if you want a smoky edge, or swap the mozzarella for Gruyere if you prefer a nuttier, more complex cheese flavor that deepens as it bakes.

Storage and Leftovers

Cover the baking dish tightly and refrigerate leftovers for up to three days, reheating individual portions in the oven at 350 degrees F so the topping stays crisp rather than turning soggy in the microwave.

• Let the casserole cool completely before covering it to prevent condensation from making the top layer soft.
• A quick sprinkle of fresh panko on top before reheating brings back the crunch beautifully.
• If freezing, skip the topping and add it fresh when you bake it from thawed.

Save

Some dishes simply make people lean back in their chairs and smile, and this golden, bubbling casserole has earned that spot at my table every single year.

Recipe Questions & Answers

→ How do I prevent soggy sprouts?

Blanch sprouts only 3–4 minutes and drain thoroughly. Drying them well and cooking the cream sauce until slightly thick helps keep the final bake from becoming waterlogged.

→ Can I make this ahead?

Assemble the casserole and refrigerate uncovered for up to 24 hours before baking. If chilled, add a few extra minutes to the bake time to ensure it heats through and the topping crisps.

→ What are good cheese substitutions?

Gruyère or Swiss work well in place of mozzarella for nuttier depth; increase Parmesan slightly for extra savory flavor. Use freshly grated cheese for the best melt and texture.

→ How do I make a gluten-free topping?

Replace panko with toasted gluten-free breadcrumbs, crushed cornflakes, or a nut-based crumble (finely chopped almonds or pecans) mixed with olive oil for a crunchy finish.

→ Best way to reheat leftovers?

Reheat portions in a 350°F oven for 10–15 minutes covered, then uncover and broil briefly to refresh the topping. Microwaving works for speed but will soften the crust.

→ Can I add protein to make it heartier?

Stir in cooked, chopped bacon or pancetta to the creamy mixture before baking for smoky richness. Cooked shredded chicken can also be folded in for a more substantial main-style dish.