How to Make It
Preheat oven to 350°F. Heat water in a saucepan with a steamer basket over medium. Cut off thick stem of cauliflower, and remove all but the smallest green leaves. Using a sharp knife, make an X in the remaining core. Place cauliflower, core side down, in steamer basket. Cover and steam until tender, about 15 minutes. Drain. Cut into florets. Transfer cauliflower to an ovenproof serving bowl.
Top cauliflower with Cheese Sauce, and sprinkle with grated cheese. Bake in preheated oven until cauliflower is heated through, cheese is melted, and sauce is light brown and bubbling, 5 to 10 minutes.
Heat butter in a skillet over medium. Add breadcrumbs; cook, stirring occasionally, until brown. Sprinkle breadcrumbs over melted cheese. Top with chopped parsley.