Easy Baked Cauliflower Gratin

This easy baked Cauliflower Gratin is a classic French side dish that's a great make-ahead recipe for serving a crowd. It's melty, cheesy and perfect for the holidays!

A gratin (pronounced grah-tahn) refers to any food that has been placed under a broiler to achieve a crispy, crunchy top, usually with either breadcrumbs, cheese, or both. "Gratin" or "au gratin" comes from the French word "grainer," which literally translates to "to broil." I've made everything from a Classic Potato Gratin to a Zucchini Gratin, a Fennel and Onion Gratin, a Parsnip and Celery Root Gratin, and a Kale Gratin, but this baked Cauliflower Gratin was the one that started my obsession.

Why this recipe works

• An authentic French gratin recipe I learned to make in culinary school.
• Utilizes the cauliflower cooking water to make the veloute sauce rather than stock or milk, which results in a lighter, cleaner flavor that actually tastes like cauliflower.
• Can be made up to two days in advance and baked before serving.
• A little cream, a lot of cheese and a buttery, garlicky, herby breadcrumb topping make this simple cauliflower bake taste amazing.

Essential Ingredients

• Cauliflower - This recipe calls for using a large whole head of fresh cauliflower, but frozen cauliflower can be used as well. Substitute about 2 ½ lbs or 6 heaping cups of frozen cauliflower florets. Having a little more or less won't affect the recipe.
• Gruyere Cheese - Look for a good quality aged Gruyere, which is the traditional French cheese used for a gratin. If Gruyere is hard to find or out of your price range, use Emmental, Jarlsberg or good quality Swiss cheese.
• Nutmeg - Freshly grated whole nutmeg is best, otherwise make sure your ground nutmeg is fresh and hasn't been sitting in your pantry for years. The flavor degrades over time so it won't have the same impact. If you can't remember when you bought it, it's time to get a new one. 
• Breadcrumbs - This cauliflower bake calls for Panko breadcrumbs because I always have them on hand and they're always light and crunchy, but homemade breadcrumbs made from stale bread would also be great.

Step by step instructions

1. Add the cauliflower to a medium pot, then add just enough room temperature water to barely cover. The goal is to use less water in order to achieve a more concentrated cauliflower flavor, so it's okay if some pieces are sticking out of the top.
2. Bring the water up to a simmer, then cover and cook until the cauliflower pieces are al dente, about 2-3 minutes. Drain the cauliflower well and reserve the cooking water.
3. Preheat the oven to 400 degrees F and butter the inside of a medium casserole dish.
4. Melt butter in a medium sauce pan over medium heat, then whisk in the flour until it absorbs all the butter, about 1-2 minutes.
5. Slowly whisk in 1 ½ cups of the reserved cauliflower cooking water (it should still be warm), then continue whisking until it comes up to a boil.
6. Lower the heat, continue whisking, and cook for 2-3 minutes until thickened.
7. Whisk in the heavy cream, salt and pepper, then turn off the heat.
8. Stir in the nutmeg and ⅓ of the Gruyere cheese (about 1 cup) until the cheese is melted. 
9. Add the well-drained cauliflower to the cheese sauce and mix to combine. Taste for seasoning and adjust as needed - it will likely need a bit more salt and pepper.
10. Scrape the cauliflower mixture into the buttered casserole dish, being sure to get every last bit of cheese sauce in there.
11. Sprinkle with the remaining Gruyere cheese, then set aside while you make the topping.
12. Melt the butter in a medium sauté pan over medium heat, then add the garlic and stir around until it starts to sizzle.
13. Add the panko breadcrumbs, thyme leaves and a pinch of salt and pepper, then continue to stir around until light golden brown, about 5 minutes.
14. Spread the breadcrumbs on top of the cauliflower in an even layer.
15. Bake for about 20 minutes, or until the breadcrumbs have darkened a few shades and it's bubbling up around the sides.
16. Allow the gratin to cool down for about 10 minutes before serving.

Tips for success

• Be careful not to overcook the cauliflower while boiling, it should still be slightly firm or al dente. The time will depend on the size of your florets - check them every minute or so with a fork.
• It's really important that the cauliflower is drained very well and does not have a lot of extra liquid before adding to the cheese sauce or it will be watery.
• Use a deep dish pie plate or cast iron skillet in place of a casserole dish if desired.

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