The only way to improve on the classic dish, in fact, is to roast the cauliflower before combining it with the lavish sauce, instead of parboiling it. This way, you get to enjoy the caramelized qualities of roasted cauliflower while also eating a lot of butter and cheese. (It’s win-win, in other words.) As with all gratins, you want your main ingredient to be fully cooked before you combine it with the topping—it will soften somewhat while it’s soaking in béchamel, but not much. The post-béchamel baking period is really just to force the ingredients to get cozy with one another, to make sure everything’s the same temperature, and to melt the cheese.
Roasted Cauliflower Gratin
Yield: 4 servings
Time: About 1 hour, partially unattended
3 tablespoons unsalted butter
1 cauliflower (about 1½ pounds), separated into florets
Salt and black pepper
1 cup whole milk
⅓ cup heavy cream
2 tablespoons all-purpose flour
½ cup grated Gruyère cheese (about 2 ounces)
1. Heat the oven to 375°F. Put 1 tablespoon of the butter in a rimmed baking sheet in the oven. When it melts, add the cauliflower, season with salt and pepper, and toss to combine. Roast, stirring occasionally, until the florets are mostly tender and lightly browned, 25 to 30 minutes. (Leave the oven on.)
2. Meanwhile, put the milk and cream in a small saucepan over low heat. As they warm up, put the remaining 2 tablespoons butter in a medium saucepan over medium-low heat. When it melts, add the flour and cook, whisking constantly, until the mixture turns golden brown, 3 to 4 minutes. Gradually whisk the warm milk and cream into the butter mixture and continue to cook, whisking frequently, until the sauce has thickened slightly, about 5 minutes.
3. Transfer the cauliflower florets to an 8- or 9-inch square baking dish. Pour the béchamel sauce evenly over the cauliflower. Sprinkle the cheese on top. Bake until the sauce is bubbling and the cheese is golden brown, about 25 minutes.
