Caramelized onions add the perfect umami touch in this Brussels sprouts gratin. They're tossed in a rich sauce of whipping cream, mustard, broth, and spices baked with a browned butter breadcrumbs topping.
Quinoa adds a protein punch to this casserole making this dish a great vegetarian main dish.
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I've yet to meet a gratin I didn't want to marry. Comfortable, unpretentious, warm, and welcoming. Some are stand-alone dishes, like this Swiss chard gratin with quinoa needing only a salad to round them out. Others show up as side dishes on a Thanksgiving table like a potato gratin or celery root gratin.
Sometimes they're healthy, sometimes not-so-much. But easily accommodate almost any vegetable, whether it's a root vegetable in winter, squash in autumn, or tomatoes in summer.
🤓 What is a gratin?
I always thought gratin meant a casserole with a cheesy baked topping. It turns out, that's almost right, but not quite.
Cooking something au gratin means to bake it with a crust made of breadcrumbs with or without cheese. The cheese isn't a critical component - the fact that the topping is scraped, shaved, or grated is what makes it a gratin.
It’s usually cooked in a shallow baking pan, often finished under the broiler for a crusty top.
Fun factoid, the term le gratin signifies the "upper crust" of Parisian society.
🧅 Main Ingredients + Notes
The secret to many dishes often lies in the ingredients. For example, some ingredients make a huge difference to the flavor and/or texture of the finished recipe. And purchasing the right ingredients can save you valuable time in the kitchen.
This list only covers ingredients that require some notes. For all of the ingredients, measurements, and directions, go to the Recipe Card at the bottom of this post.
- Brussels Sprouts – Purchase the freshest looking Brussels sprouts you can. Ideally, purchase them still on the stalks. If they’re not available that way, select them individually instead of in a net bag already gathered together.
- Quinoa – If you’re not a quinoa fan, substitute rice, farro, or barley. But you’ll sacrifice the protein of the quinoa.
- Vegetable broth – Either use homemade vegetable broth or Better Than Bouillon – Roasted Vegetable Paste. For every cup of vegetable broth called for, dilute 1 teaspoon of Bouillon paste into hot water. If using Bouillon paste, eliminate additional salt.
- Celery Salt – This ingredient is important to the overall flavor of the gratin as it’s a fabulous partner with Brussels sprouts. Even if you eliminate the kosher salt, don’t eliminate the celery salt.
Disclosure: This post may contain affiliate links to products and foods I use in my kitchen. This means that at no additional cost to you, I will earn a commission if you click through and make a purchase. To view my entire storefront of recommended kitchen tools and equipment, check out my shop on Amazon.
🔪 Recommended Equipment
Having the right equipment for recipes makes prepping much easier. If you want more fuss-free prepping and cooking, check out my updated list of favorite kitchen tools and equipment.
- Medium bowl – for rinsing the quinoa seeds.
- Colander – for rinsing and draining the quinoa.
- Large pot – for cooling the quinoa.
- Food processor fitted with a grater – for slicing the Brussels sprouts.
- Chef’s knife – for slicing the Brussels sprouts if you don’t have a food processor.Using a chef’s knife allows for thicker slices of Brussels sprouts, which will take longer to cook.
- Large bowl – for combining all of the ingredients.
- Medium skillet – for reducing the broth and whipping cream mixture.
- Casserole dish – I recommend one that is 11 inches X 13 inches. If you use a 9 inch X 11 inch casserole dish, cook for an additional 10 minutes.
- Small bowl – to mix the gratin topping.
⏰ Tips to Simplify and Save Time
- Make the quinoa ahead of time, and store in an airtight container in the refrigerator for up to 5 days.
- Make the caramelized onions ahead of time and store in an airtight container in the refrigerator for up to one week.
- Some markets sell frozen cooked quinoa in their freezer cases. It only needs to be steamed for a few minutes to be ready to use.
- Use the food processor fitted with a grater to slice the Brussels sprouts. It’s super-fast. Or purchase Brussels sprouts already sliced. Many grocery produce departments sell them like this in refrigerator cases.
- I have not made this casserole with frozen sliced Brussels sprouts, but it should be fine to use them. Thaw them before tossing with the remaining ingredients.
Ways to Use Gratins
- Gratins are perfect for leftover vegetables like cauliflower, broccoli, spinach greens, and potatoes, or pasta. But don't think you can use vegetables that are too far past their prime.
- Gratins are ideal for vegetables and greens on the bitterness spectrum. I'm thinking Brussels sprouts, or winter greens like kale, Swiss chard, and mustard greens. Another excellent candidate for casseroles is broccoli rabe, as famous for its bitterness as for its nutritional profile.
- I often make gratins for casual dinner parties, and cook them ahead earlier in the day. All I need do is warm them up as guests arrive.
More Brussels Sprouts Recipes
Another main dish with Brussels sprouts is these pan-roasted Brussels sprouts with eggs. The Brussels sprouts are caramelized with balsamic vinegar and red onions, and topped with poached eggs.
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Brussels Sprouts Gratin with Quinoa
Equipment
- 9" X 11" casserole dish
- Food Processor optional for slicing the Brussels sprouts
- Large bowl
- Small skillet to make the browned butter breadcrumbs
Ingredients
Brussels Sprouts
- 1 large yellow onion, thinly sliced
- 4 tablespoons unsalted butter, divided
- 1 cup cooked quinoa
- 2 pounds Brussels sprouts hard stem bottoms trimmed
- 1 cup dried cranberries
- 1 cup vegetable broth
- ½ cup heavy whipping cream
- 1 tablespoon Dijon mustard
- 1 teaspoon celery salt
- ¼ teaspoon ground black pepper
- ¼ teaspoon kosher salt
- 1 ½ cups browned butter breadcrumbs
Instructions
- Preheat oven to 350º F and butter a casserole dish.
- Peel and slice a large yellow onion in half around its middle. Thinly slice. Melt 2 tablespoons of the butter in a medium-large skillet over medium heat and add the onion slices all at once. Use tongs to toss a bit in the butter.After a few minutes, the onions will relax into the skillet. Reduce the heat to medium-low and sauté the onions until lightly browned without moving them around much if at all. Once they begin to brown, toss them in the skillet, and allow them to further brown. They brown best when they aren't moved around the skillet very often. Continue to cook until the onions are caramelized a deep brown. This can take as long as one hour when cooked slowly. Alternatively keep the stovetop burner on medium, but keep your eye on the onions as they'll may burn.
- If you don't have any cooked quinoa on hand, rinse some quinoa seed and set it on the stove to simmer. Follow these directions for my best cooked quinoa.
- Thinly slice the Brussels sprouts using the slicing disc of a food processor or slice them thicker using a sharp chef's knife. Dump into a large bowl and add the cranberries, caramelized onions, and cooked quinoa.
- Melt 2 tablespoons of the butter in the same medium skillet used to caramelize the onions and add the broth, whipping cream, mustard, celery salt, kosher salt and pepper. Whisk and heat just until starting to simmer. Pour over the Brussels sprouts quinoa mixture and toss to completely coat.Pile the mixture into the buttered casserole dish and spread in an even layer.
- Bake the gratin until the Brussels sprouts are tender, about 45 minutes.
- Make the browned butter breadcrumbs and spread over the top of the Brussels sprouts for a nice crunch before serving. Or toss Panko breadcrumbs in melted butter, salt and pepper and spread over the Brussels sprouts before sliding into the oven. Serve warm.
Renee - Kudos Kitchen
I love the addition of heavy cream to make this dish healthy and sinful! It's the best of both worlds! Nice recipe. Can't wait to try it.
The Wimpy Vegetarian
I couldn't be completely healthy with this, lol.
Laura Dembowski
My love of Brussels sprouts knows no end. This is such a creative way to use them.
The Wimpy Vegetarian
Thanks so much Laura! Ours is a big Brussels sprouts household too 🙂
Liz
Mmmmm....I love absolutely everything about this casserole. I wouldn't want to share this one!!!
The Wimpy Vegetarian
Thanks so much Liz! I've made it 3 times in the past 10 days to get it where I wanted, and each time it disappears like magic!
Velva-Tomatoes on the Vine
This is a beautiful dish. Love, love it. Thanks for sharing it with your readers.
Velva
The Wimpy Vegetarian
Thanks so much!!
Jude
If this is the Wimpy Vegetarian --- why is there 5 slices of bacon in the recipe??
The Wimpy Vegetarian
Because they're optional - I give alternate instructions in the notes. And I'm a wimpy vegetarian. In my "About" page, I'm honest that I'm not a complete vegetarian 🙂
marye
I'll eat brussels sprouts just about any way you want to serve them - pairing them with quinoa is such a great idea!
The Wimpy Vegetarian
Thanks so much Marye. I keep cooked quinoa in the fridge pretty often, and tend to add it to all kinds of things!
Nikki
Brussels Sprouts are a favorite of mine. The addition of cranberries and quinoa just sounds amazing! Beautiful dish!