Cauliflower Gratin

Adjust oven rack to middle position and preheat the oven to 375ºF (190ºC). Line a large rimmed baking sheet with parchment paper; spread cauliflower in an even layer. Season to taste with salt. Bake cauliflower until starting to brown, 30 to 35 minutes, stirring halfway through. Set aside.

Meanwhile, for the Breadcrumb Topping: In a small bowl, stir together melted butter, breadcrumbs, and za’atar until well combined. Season to taste with salt. Set aside.

For the Mornay Sauce: In a medium bowl, whisk together 2 tablespoons of the half and half with the miso paste until thoroughly mixed. Stir in remaining 2 3/4 cups plus 2 tablespoons half and half; set aside.

In a medium saucepan set over medium heat, melt 4 1/2 tablespoons butter. Add flour and whisk to form a paste. Continue to cook, stirring, until raw flour scent is gone, about 1 minute. Whisking constantly, add miso mixture in a thin, steady stream, or in increments of a couple of tablespoons at a time, whisking thoroughly and getting into all corners of the pan to maintain a homogeneous texture. (The sauce will initially become very thick, then get very thin once all the half and half is added.) Heat, stirring often, until sauce comes to a simmer and begins to thicken slightly, about 5 minutes. Reduce heat to low and cook, stirring, until sauce is thick enough to coat the back of a wooden spoon, about 3 minutes. Remove from heat, then stir in the bay leaves, onion powder, garlic powder, and white pepper until well-combined. Stir in Gruyère and Parmigiano-Reggiano until just combined. Season to taste with salt.

Transfer cauliflower to a 9- by 13-inch baking dish or pan and season with salt and freshly ground pepper. Pour the Mornay sauce evenly over the cauliflower and evenly sprinkle the breadcrumb mixture all over. Bake, uncovered, rotating dish halfway through, until the sauce is bubbling around the edges and breadcrumbs are lightly golden brown, 10 to 12 minutes.