1 large head (about 680 grams) cauliflower (broken into florets)
For the Sauce
2 cups (454 grams) whole milk
4 tablespoons all-purpose flour
4 tablespoons unsalted butter
1/2 teaspoon Dijon or English mustard (optional)
6 ounces sharp cheddar cheese (shredded, divided)
Kosher salt (to taste)
Freshly ground black pepper (to taste)
Instructions
Prepare the Pan and Topping: Heat the oven to 425 F (220 C) and butter a 1 1/2-quart baking dish with 1 teaspoon of butter. Melt the remaining 2 teaspoons of butter and toss with the panko crumbs. Set aside.
Boil the Cauliflower: Bring a pot of water to a boil. Add the cauliflower. Boil for 5 minutes. Drain well and transfer it to the prepared baking dish.
Make the Sauce: Melt the 4 tablespoons of butter over medium heat in the same pot or a medium saucepan. When the butter sizzles, add the flour. Cook, whisking constantly, for 2 minutes. Gradually whisk in the milk and mustard (if using), and continue cooking while constantly whisking until thickened. Add 1 cup (about 4 ounces) of the shredded cheese and cook until thickened and the cheese has melted. Taste and season with salt and pepper.
Finish the Dish: Pour the cheese sauce over the cauliflower florets and top with the remaining cheese. Sprinkle with the buttered panko crumbs.
Bake: Bake the cauliflower cheese for 15 to 18 minutes or until bubbling and browned.