Preheat the oven to 375 degrees F. Coat a large baking dish with nonstick cooking spray.
Bring water to a boil in a large pot over HIGH heat. Add the cauliflower florets and cook until just barely tender, about 5 to 6 minutes. Drain, and set aside.
Meanwhile, melt the butter in a medium saucepan over LOW heat. Add the flour and cook, whisking, for about two minutes. Gradually whisk in the warm milk. Continue to cook, whisking, until thickened. Add 1 teaspoon of salt, ½ teaspoon pepper, and nutmeg, and stir to combine. Remove the pan from the heat and add the shredded cheese.
Pour the sauce over the the cooked cauliflower and mix well to combine. Pour the cauliflower mixture into the prepared baking dish.
Combine the bread crumbs with the Parmesan and sprinkle the mixture evenly over the top. Sprinkle with additional pepper, if desired. Bake for 25 to 30 minutes, until golden brown and bubbly.
