Roasted Cauliflower Gratin

Rich and decadent cauliflower gratin is a great side dish for holiday dinners. Roasted cauliflower is combined with a cheddar cheese sauce flavored with onion and garlic. Make it for Easter, Thanksgiving, Christmas, or other special occasions.

cauliflower gratin in a baking dish.

A holiday table or other celebration meal is not complete without a gratin, which is just a dish – in this case, roasted cauliflower – that is baked with a sauce and cheese or breadcrumbs on top.

And so for this roasted cauliflower gratin, we start with a classic bechamel sauce that, up until now, I thought was just a simple combination of milk, flour, and butter.

Homemade Béchamel Sauce

When I set out to learn about the five mother sauces, I was excited about all of them except one – bechamel. What’s to get excited about? I’ve made it a thousand times (mac & cheese is a lifelong love), so my initial thought was  “how boring.”

My plan was to sort of slip it in on my way to more exciting parts of this series (bring on the classic tomate and espagnole sauces!). However, despite my dead-beat approach to making bechamel, I did do my research and – lo and behold – I learned some things! And I used the bechamel sauce to make a rich and comforting roasted cauliflower gratin.

Notes About the Sauce

So, I was surprised to learn that a lot of bechamel recipes call for an onion that you simmer in the butter, flour, milk mixture. 

I’ve never done that before and you might think it makes it all onion-y weird, but it doesn’t and the sauce ends up with just a subtle hint of onion.

Many classic recipes also call for one whole clove that you stick in the onion. I’ve done it with and without the clove and I honestly can’t tell the difference. So my bechamel is sans clove.

Ingredients for the dish.


  • Unsalted butter
  • All-purpose flour
  • Whole milk
  • Onion wedge
  • Cauliflower florets
  • Whole head of garlic
  • Olive oil
  • Shredded cheddar cheese
  • Salt and pepper

I learned I’ve been making bechamel wrong my whole life. Or I should say, I’ve been way too loosey- goosey with my bechamel up until now. I never paid much attention to the ratio of butter/flour/milk preferring to instead fly to by the seat of my pants.

I also learned you have to take your time (I’ve always rushed through the process before) and, by the way, that time investment is so worth it – the resulting sauce was so creamy and had the most amazing consistency. Like, “Can I just drink that straight from the saucepan” amazing.

How to Make Cauliflower Gratin

For this gratin, we are roasting cauliflower florets and garlic until they are caramelized and delicious. Roast them at 425°F for about 30 minutes.

cauliflower and garlic on a sheet pan.

While the cauliflower and garlic are roasting, you can make the cheese sauce, starting with a classic bechamel.

First, melt the butter in a saucepan. You want the sauce very white (hence its nickname ‘white sauce’), so melt the butter over pretty low heat before adding the flour to make the roux (a lesson I learned after making veloute sauce).

Next, you add milk and whisk until you have a smooth, white sauce. Add the onion wedge and cook the sauce until it’s thick enough to coat the back of the spoon.

Once the sauce is thickened, discard the onion. Squeeze the cloves out of the roasted garlic and mash them up. Add them to the sauce and stir.

To turn it into a cheese sauce, all you do is add… yes, cheese. Cheddar cheese. Add it and stir until it’s melted into the sauce.

Add the roasted cauliflower florets to the sauce and then pour it all into a baking dish.

Sprinkle more cheese over the top and place the baking dish under the broiler until the cheese is melted and the gratin is bubbling hot.

the gratin ready to go in the oven.

This recipe easily stretches to serve six if it’s served with other side dishes. It’s very rich and decadent so a little goes a long way. That said, you can easily double it if you want bigger servings or to serve more people.

It’s definitely what I consider “celebration food” – you know, a dish that is perfect for a holiday dinner like Easter or Thanksgiving. It’s a great side dish for ham or turkey.

Happy cooking,

overhead shot of roasted cauliflower gratin in baking dish.

More Decadent Side Dishes


Roasted Cauliflower Gratin

cauliflower gratin

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5 from 4 reviews

Creamy, cheesy roasted cauliflower gratin. This is a rich and decadent side dish that is great for holiday celebrations.

  • Author: April Anderson
  • Prep Time: 15 minutes
  • Cook Time: 45 minutes
  • Total Time: 60 minutes
  • Yield: 6 servings 1x
  • Category: Side Dish
  • Method: Bake
  • Cuisine: American


  • 2 tablespoons unsalted butter
  • 1/3 cup all-purpose flour
  • 2 1/2 cups whole milk
  • 1/4 of an onion (wedge)
  • 1 head of cauliflower, broken down into 2-inch florets
  • 1 head of garlic
  • 2 tablespoons olive oil, plus 1 teaspoon
  • 2 cups shredded cheddar cheese
  • 1/2 teaspoon kosher salt
  • 1/4 teaspoon pepper


  1. Preheat oven to 425°F. Toss the cauliflower florets with 2 tablespoons of olive oil and a couple pinches of salt and pepper. Spread the florets evenly on a baking sheet.
  2. Cut just the top off the head of garlic (enough to expose the cloves), drizzle 1 teaspoon of olive oil over the top, and then wrap the garlic in tin foil. Place it on the sheet pan with the cauliflower.
  3. Roast the garlic and cauliflower for about 30 minutes, just until the cauliflower is tender and nicely browned in places.
  4. While the cauliflower is roasting, prepare the bechamel sauce. First, heat the milk in a saucepan until it just starts to simmer.
  5. While the milk is heating, in another saucepan melt the butter over low heat until frothy. Sprinkle in the flour and stir until it forms a paste.
  6. Slowly pour in the hot milk, whisking continuously to ensure no lumps form and the roux fully incorporates into the milk. Raise the heat to bring the pot to a simmer.
  7. Place the onion wedge in the milk mixture. Let the mixture simmer and thicken for about 20 minutes or so, or until it has reduced enough to coat the back of a spoon. You will need to stir frequently to ensure the bechamel does not burn on the bottom of the pan. Once thickened remove the onion. If your sauce has lumps you can strain it, but this is optional.
  8. Squeeze out the cloves and mash them with a fork. Add the garlic to the sauce and stir to combine.
  9. Stir in 1 1/2 cups of the grated cheese until it’s melted into the sauce. At this point taste for seasoning and add in some salt and pepper (I added 1/2 teaspoon of salt and 1/4 teaspoon of pepper, but season to your taste).
  10. Gently fold the roasted cauliflower florets into the sauce. Pour the mixture into an 8 x 8 baking dish, top with the remaining cheese. Place it under the broiler until the cheese melts and starts to brown a bit on top. Remove from the oven and serve.


You can roast the cauliflower ahead of time following the instructions and keep it in the refrigerator for up to a day. Instead of placing the baking dish under the broiler, preheat the oven to 350 degrees and bake the dish for 20 to 30 minutes or until it’s bubbling and hot.


  • Serving Size: 1/6 of recipe
  • Calories: 342
  • Sugar: 6.3g
  • Sodium: 498.7mg
  • Fat: 25.4g
  • Saturated Fat: 12.2g
  • Unsaturated Fat: 10.8g
  • Trans Fat: 0.3g
  • Carbohydrates: 16g
  • Fiber: 1.3g
  • Protein: 13.9g
  • Cholesterol: 57.6mg

Do you love this recipe? Don’t forget to leave a comment and your recipe star rating!

Post, photos, and recipe were updated in March 2021.


  1. Wow! Nice lesson in bechamel sauce. I learned a few things here. The clove onion thing is totally new to me. Looks like I better make this recipe. Cheese, cauliflower and white sauce….great idea!

  2. I just made this for Canadian Thanksgivig and it was incredible! Thank you! The onion and roasted garlic definitely took this to the next level of flavour. This is a keeper.

  3. Hi, just a quick tip. I use a whisk to stir my sauce, as a result I don’t get lumps. You also need to cook the roux for 1 minute to avoid the grainy flour texture.

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