Cheesy Brussels Sprouts au Gratin

At a glance

What stands out: Bubbling with a creamy Gruyère sauce, cheesy Brussels sprouts au gratin is irresistible. A reliable dish to serve for Thanksgiving but don’t wait that long to try this rich gratin.

How long it takes: 15 minutes to prep, 40 minutes to bake
Equipment you’ll need: 9 x 13 inch baking dish, saucepan
Servings: 8

We can’t believe we’re thinking about Thanksgiving already! It seems like we were just talking about inflatable rafts and sunscreen lotion.

Only take a look at the shelves in your grocery store though, and you’ll know that fall has arrived. All of the cool weather crops are displayed, inviting us to make the transition from summer eating (watermelons, cucumbers, corn on the cob, strawberries!) to autumn foods: winter squash, apples, pumpkins, cabbage, and Brussels sprouts. We love the flavors of fall, don’t you?

We especially love these cheesy Brussels sprouts! Roasted lightly, then smothered with a creamy Gruyère cheese sauce, with a hint of nutmeg and thyme, and baked again until lightly browned and bubbling, these Brussels sprouts are a culinary delight!

About This Brussels Sprouts Gratin

Cheesy Brussels sprouts are a “gratin”. What does gratin mean? In French, “au gratin” means “by grating.” In traditional French cooking, a gratin is a made in a shallow dish containing potatoes, vegetables, or even seafood, covered with a lightly browned crust of bread crumbs or cheese.

Au gratin can also mean casserole, or scraping from the pan, and we guarantee you’ll be scraping the pan of this Brussels sprouts gratin for every last rich morsel.

Seriously, when we were testing this recipe, we could hardly wait for this casserole to come out of the oven and we weren’t disappointed! Even people who are professed Brussels sprouts haters will be converted by the creaminess and flavor of this mouthwatering gratin.

Brussels or Brussel

There is some confusion about how to spell the name of this tiny green cabbage-like vegetable. Many people use the spelling Brussel sprouts, omitting the “s” at the end of the word Brussels. Brussels sprouts are actually named for the Belgium city of Brussels so you definitely spell it with the “s” at the end. We don’t want to offend the good people of Brussels!

What goes in

• Brussels Sprouts: Look for fresh, firm dark green sprouts. You’ll need 2 bags, or about two pounds.
• Olive Oil, Salt, Pepper: The Brussels sprouts are seasoned with salt and pepper and tossed with a bit of oil before roasting.
• Onion: A yellow cooking onion is fine for this recipe; other types of onion work too.
• Butter, Flour, Whole Milk: This trio makes up the simple white sauce which is the base of the gratin.
• Thyme: Use fresh if you can but dried is fine, too. Use less if you’re using dried thyme because it’s more potent than fresh.
• Nutmeg: Freshly grated nutmeg is so much better tasting than ground nutmeg! Look for whole nutmeg and use a fine grater.
• Gruyère cheese: This hard cheese is a type of Swiss cheese. It is more dense and doesn’t have large holes like typical Swiss cheese. It melts easily and has a sharper flavor.

How To Prep Brussels Sprouts

Prepping and pruning those tiny green cabbages can seem tricky the first time you do it.

• Look for firm, compact, dark green Brussels sprouts that don’t have worm holes, aren’t shriveled, or have yellowing loose leaves.
• Rinse them well in a colander under running water.
• Using a sharp paring knife, cut off the tough stem, about even with the edge of the sprout.
• Peel away discolored or wilted outer leaves.
• For this recipe, cut the sprouts in half lengthwise. Whether or not you cut your sprouts depends on their size. You want them to be uniformly bite-sized. Just remember: Halving the sprouts allows the cheesy sauce to permeate each tasty morsel!
• If you’d like a visual of how to prep Brussels sprouts, take a look at this informative YouTube video.

How it comes together

Prep all of the ingredients. You’ll want to have all the ingredients for making this recipe prepared before you begin cooking it. Prep the Brussels sprouts, grate the Gruyère, measure the milk, flour, and butter for the white sauce, grate the nutmeg, and chop the thyme.

Preheat the oven and choose a dish. Get your oven preheating to 400ºF and prepare your baking dish. You’ll want to use a nice looking shallow glass dish for this recipe because you’ll be serving the gratin right from the dish.

Roast the Brussels sprouts. Toss the prepped Brussels sprouts with a bit of olive oil, season with salt and pepper, spread them in the baking dish, and roast for about 20 minutes, or until they’re just beginning to brown slightly.

Make the cheese sauce. Meanwhile, prepare the white sauce on the stovetop, whisking in the cheese, nutmeg, and herbs when the sauce has thickened.

Bake. Pour this creamy cheese sauce over the sprouts (you might want to reserve a spoonful or two for tasting because it’s soooo good), sprinkle the top with additional grated Gruyère, and pop the dish back into the oven for 20 minutes or so, until it’s brown and bubbling.

Cool before serving. Let the casserole cool for 5 to 10 minutes before serving. Serve it right from the baking dish.

Ways to change it

• Try a different cheese. The slightly nutty flavor of Gruyère is reliable in this gratin but other types of cheese can be substituted: Swiss cheese, sharp cheddar, Parmesan or Asiago.
• Add bacon or pancetta. Just cut it into 1 inch pieces, cook until done, drain, and add it with the cheese.
• Experiment with the spices and herbs. If you love garlic, try adding a bit of garlic powder to the white sauce. Paprika is a good addition, as well, maybe sprinkled on the top to add a little color. If you’re not a nutmeg fan, leave it out. It will still taste great!
• Lighten it up by using low fat milk to make the white sauce. It won’t be quite as creamy but you’ll save some calories and fat. If you’re looking to cut calories, don’t mix any cheese into the white sauce and just sprinkle a half cup on top of the gratin before baking.
• Not a fan of Brussels sprouts? Try scalloped sweet potatoes with bacon and Gruyère instead. Asparagus casserole is pretty memorable, too.

Make-Ahead Ideas

Get a head start: Prep the Brussels sprouts up to two days ahead. The onions can be chopped ahead too. Store separately in covered bowls or resealable bags in the refrigerator. Shred the cheese and store in the refrigerator for up to a week.

Keeping leftovers

This dish is best eaten right away. If you do have leftovers, heat them gently in the oven until they’re heated through, or in the microwave. The gratin will keep a couple of days in the fridge.

Special Occasion Side Dishes

• Yield: 8
• Prep: 15 minutes
• Cook: 40 minutes
• Total: 1 hour 5 minutes

Ingredients

• 2 pounds Brussels sprouts
• 1 tablespoon olive oil
• ¼ teaspoon kosher salt
• ⅛ teaspoon ground black pepper
• 2 tablespoons unsalted butter
• ½ cup diced yellow onion (about ½ medium onion)
• 2 tablespoons all-purpose flour
• 1 ¾ cups whole milk
• 1 teaspoon roughly chopped fresh thyme (or ½ teaspoon dried thyme)
• ¼ teaspoon freshly grated nutmeg
• 4 ounces Gruyère cheese, shredded and divided

Method

1. To prepare Brussels sprouts, rinse well. Trim off bottom (stem) end and remove any brown or tough outer leaves. Cut in half from top to bottom.
2. Preheat oven to 400ºF. Spray a 9 x 13-inch baking dish with nonstick baking spray.
3. Mix Brussels sprouts with olive oil, salt, and pepper, and add to prepared baking dish. Bake for 20 minutes or until starting to brown. Remove from oven.
4. While Brussels sprouts are roasting, in a medium saucepan over medium heat, melt butter. Add onions and sauté, stirring constantly, until translucent, or about 2 minutes. Add flour and continue to stir or whisk for 1 minute.
5. Slowly add the milk, stirring constantly, and cook over medium-low heat until thickened, 10 to 12 minutes. Remove from heat.
6. Add thyme and nutmeg to the sauce, and stir to combine. Stir in half of the cheese until melted. Pour cheese sauce over Brussels sprouts, stirring lightly to combine. Top with remaining cheese.
7. Bake for 20 minutes, or until top is starting to brown and gratin is bubbling.
8. Let cool 5 to 10 minutes before serving.

Notes

With bacon or pancetta. If desired, add bacon or pancetta to the gratin. Cook diced bacon or pancetta until crisp, drain well, and stir into the sauce with the thyme and nutmeg.

Cheese variations: Other types of cheese can be substituted. Try Swiss cheese, sharp cheddar, Parmesan or Asiago.

Make ahead tip: Prep Brussels sprouts and onion and store in separate containers in the refrigerator up to two days in advance. Shred cheese up to a week in advance.