Broccoli and Cauliflower Gratin

Broccoli and Cauliflower Gratin decks out tender crisp vegetables in a velvety hug of savory cheese sauce with bright accents of wine, Dijon, and thyme. This easy to prepare casserole is special enough for any holiday feast while being a great addition to any Sunday meal.

Broccoli and Cauliflower Gratin

Cheese makes everything better including humble cruciferous veggies like broccoli and cauliflower. Nutty, salty, and rich Gruyère is combined with the umami of Parmigiano-Reggiano for a one two punch of bold flavor that perfectly accents both vegetables. Serve this up with your Christmas prime rib or Sunday bourbon glazed meatloaf.

Why You’ll Love This Recipe

Broccoli and Cauliflower Casserole
  • Make Ahead – Not only can you blanch your vegetables ahead of time, but you can also assemble this broccoli and cauliflower casserole a day or two in advance and then bake it off when you’re ready.
  • Texture – Because the vegetables are quickly blanched, they still retain their integrity of texture. No mushy broccoli here! The cheese sauce itself is also smooth and silky without being gloopy. There is just enough to hug all of the vegetables.
  • Simple Ingredients – Aside from the two types of cheese, the rest of the ingredients for this broccoli cauliflower au gratin are budget friendly and probably kitchen staples you already have like garlic, flour, and butter. This is as easy to shop for as it is to make.

Ingredients

Ingredients for Broccoli Cauliflower Gratin
  • Broccoli/Cauliflower Fresh is absolutely best for this recipe as you’ll not only get the best flavor but also the best texture.
  • Aromatics – Shallots and garlic add layers of savory flavor to the mornay sauce.
  • Milk – For the best flavor and texture use whole milk. This will give you a luscious sauce with rich flavor.
  • Cheeses – Gruyère is the ideal melting cheese for the sauce and adds incredible flavor to the topping. Parmigiano-Reggiano makes the cheese sauce extra rich and savory and doesn’t require a lot.
  • Flavor Accents – White wine, Dijon mustard, and lemon zest add a bright note that balances the richness while crushed red pepper flakes add a back note of heat and thyme adds lemony, woodsy freshness.
  • Topping – Down here in the south we love a good crunchy topping on any and all of our casseroles. This cheesy broccoli and cauliflower gratin gets a topping that combines butter crackers such as Ritz or Club crackers with Gruyère, fresh thyme, and crushed red pepper flakes.

How to Make Broccoli and Cauliflower Gratin

  • Parboil the broccoli and cauliflower. Bring a large pot of water to a boil and add salt. Add the broccoli and cauliflower and allow it to boil for 4-5 minutes until the broccoli is bright green and the vegetables are just fork tender. Drain and allow them to cool.
  • Sauté the shallots and garlic. Heat a large skillet over medium heat and let the butter melt. Add the diced shallots, garlic, salt, and pepper. Let them cook until the shallots are translucent and the garlic fragrant, 3-5 minutes. Add the crushed red pepper flakes and stir.
  • Make the roux. Add the flour and stir it in. Let it cook for 2-4 minutes until a light golden color with a slightly nutty aroma.
  • Next make the béchamel sauce. Slowly pour in the wine while continuously stirring. Allow it to cook for one minute. Pour in a third cup of milk at a time, stirring to incorporate before adding the next. Allow the sauce to come to a simmer, stirring often, and cook until thickened, about five minutes.
  • Turn the béchamel sauce into a mornay sauce. Once the sauce has thickened turn the heat to low and stir in the cheese and fresh thyme. Keep stirring until it has completely melted. Finally stir in the Dijon mustard and lemon zest. Taste and adjust seasoning if needed.
  • Fold in the drained broccoli and cauliflower. Turn off the heat.
  • Make the butter cracker cheese topping. Add the crackers, cheese, crushed red pepper flakes, and thyme to a food processor and pulse until it’s a fine sand texture.
  • Assemble the casserole. Brush an oven or grill safe baking dish with olive oil. Pour the broccoli and cauliflower casserole mixture into the pan. Sprinkle the cracker topping over the top.
  • Bake until golden and bubbly. Allow the cheesy broccoli and cauliflower casserole to bake in a 400 degree oven for 20-25 minutes until golden. If making this on the grill bake indirect using the two zone method, rotating the casserole once or twice.

Variations & Substitutions

Broccoli and Cauliflower Bake
  • For an even more decadent dish use heavy cream instead of whole milk. You can also use one cup of each.
  • If you don’t cook with wine use the same amount of either chicken broth or vegetable broth.
  • Swap out the cheese. Instead of Gruyère use white cheddar, Jarlsberg, or Emmental. There are also some brand specific options that are really good. Cabot has an Alpine cheddar that works well in this. There is also a cheddar Gruyère from Wood River Creamery that is delicious.
  • Feel free to use all cauliflower or all broccoli in this recipe.
  • Love mushrooms? Add eight ounces of sauteed mushrooms to this recipe. Sauté them first and then add the shallots and garlic.
  • If you really want to take this over the top add four strips of cooked, chopped bacon. Fold it into the sauce when adding the broccoli and cauliflower.
  • Switch up how you cook the broccoli and cauliflower. You can also steam it or roast it. Just make sure to cook it until just tender-crisp as it will continue to cook more in the oven.
  • Replace the shallots with a sweet onion. You’ll need about 1/2 cup diced sweet onion.

Tips From the Beach

Broccoli and Cauliflower Gratin
  • This cauliflower and broccoli casserole can be assembled two to three days in advance. Hold off making and adding the cracker topping until just ready to bake. Make sure to keep the casserole dish tightly covered in the refrigerator. You may need to add about five minutes more bake time if baking from cold depending on your oven.
  • Cauliflower tends to cook a little faster than broccoli. Because of this you may want to make your cauliflower florets a little chunkier than the broccoli florets.
  • Don’t toss the broccoli stems out! Give them a peel and chop them up. They add texture and a slightly different flavor to this vegetable gratin.
  • If making this on the charcoal grill, sprinkle on a few wood chips to give this a layer of smoky flavor.

Can I use frozen broccoli and cauliflower for broccoli and cauliflower gratin?

You can, but the texture will be a little softer. You will need a bag of each. Cook them according to the package directions and then pat them dry.

What is the difference between a béchamel sauce and a mornay sauce?

Both of these sauces are classic French sauces. A béchamel sauce is a milk-based sauce that is thickened with a roux, or flour and butter/oil/fat mixture. A mornay sauce has the addition of cheese, usually Gruyère or parmesan. You start by making the béchamel and then when you add the shredded cheese is becomes a mornay sauce.

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Broccoli and Cauliflower Gratin

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Broccoli and Cauliflower Gratin decks out tender crisp vegetables in a velvety hug of savory cheese sauce with bright accents of wine, Dijon, and thyme.

  • Author: Nicole Stover
  • Prep Time: 20
  • Cook Time: 25
  • Total Time: 45 minutes
  • Yield: 4-6 1x
  • Category: Side Dish
  • Method: Baking
  • Cuisine: American

Ingredients

Units Scale

Broccoli and Cauliflower Gratin

  • 1 large head cauliflower, broken into florets
  • 1 bunch broccoli (usually 23 heads per bunch) broken into florets, stems peeled and chopped
  • 1/4 cup unsalted butter
  • 2 shallots, diced
  • 2 garlic cloves, minced
  • 1/2 teaspoon kosher salt
  • 1/4 teaspoon crushed red pepper flakes or more to taste
  • 1/4 teaspoon black pepper
  • 3 tablespoons All Purpose flour
  • 1/3 cup dry white wine
  • 2 cups whole milk
  • 1/2 cup Gruyère cheese, shredded
  • 1/4 cup Parmigiano-Reggiano, shredded
  • 1 teaspoon Dijon mustard
  • 1 teaspoon fresh thyme, chopped
  • 1 teaspoon lemon zest

Topping

  • 1 cup butter crackers (such as Ritz or Club crackers)
  • 1/2 cup Gruyère cheese, shredded
  • 1 teaspoon fresh thyme, chopped
  • 1/4 teaspoon crushed red pepper flakes

Instructions

  1. Bring a large pot of water to a boil and salt. Once boiling add the broccoli and cauliflower and allow it to blanch for 4-5 minutes until the broccoli is bright green and they’re just fork tender. Drain and let cool.
  2. Preheat the oven or grill to 400 degrees. If making this on the grill prepare your grill for two zone cooking as this will bake indirect. Brush a casserole dish or grill safe pan with olive oil and set aside.
  3. Heat a large skillet over medium heat and melt the butter. Add the shallots, garlic, salt, pepper, and crushed red pepper and sauté for 3-5 minutes until the shallots are translucent and the garlic is fragrant.
  4. Sprinkle the flour over the shallot/garlic mixture and cook for 2-4 minutes until slightly golden and nutty smelling.
  5. Slowly pour in the wine stirring constantly. Let it cook for 1 minute.
  6. Add the milk 1/3 cup at a time, stirring constantly. Wait to add the next until it’s all incorporated. Once you have added all the milk keep stirring until the sauce has thickened and coats the back of the spoon, about 5 minutes.
  7. Turn the heat to low. Stir in the cheeses and thyme. Keep stirring until the cheese has melted.
  8. Add the Dijon mustard and lemon zest. Taste the sauce and add additional seasoning if needed.
  9. Turn off the heat. Fold in the drained cauliflower and broccoli. Pour the gratin mixture into the prepared casserole dish.
  10. To make the cracker topping add all of the topping ingredients to a food processor. Pulse until a fine sand texture. Sprinkle the mixture over the casserole.
  11. Allow the gratin to bake for 20-25 minutes until the top is golden and the sauce is slightly bubbly. If making this on the grill place on the cooler, indirect side. You will want to rotate it once or twice so it browns evenly.

Notes

  1. For a richer sauce replace the milk with heavy cream. You can also do one cup milk, one cup heavy cream.
  2. If you don’t cook with wine, you can replace the wine in this recipe with either chicken broth or vegetable broth.
  3. Switch up how you cook the broccoli and cauliflower. You can also steam it or roast it. Just make sure not to overcook it as it will cook more in the oven.

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