CAULIFLOWER CHEDDAR GRATIN WITH HORSERADISH CRUMBS

Steps:

• Preheat oven to 450°F. Butter a 2-quart shallow baking dish.
• Cook cauliflower in a 5- to 6-quart pot of boiling salted water until just tender, 6 to 8 minutes. Drain cauliflower well in a colander and transfer to baking dish.
• While cauliflower cooks, melt 2 tablespoons butter in a 3- to 4-quart heavy saucepan over moderately low heat and whisk in flour. Cook roux, whisking, 3 minutes. Add milk in a slow stream, whisking, and bring to a boil, whisking frequently. Reduce heat and simmer sauce, whisking occasionally, 8 minutes. Remove from heat and add cheese, scallion greens, salt, and pepper, whisking until cheese is melted. Pour cheese sauce over cauliflower and stir gently to combine.
• Coarsely crumble crackers into a bowl. Melt remaining 2 tablespoons butter in a small saucepan, then remove from heat and stir in horseradish. Pour over crumbs and toss to coat.
• Sprinkle crumb topping evenly over cauliflower.
• Bake gratin until topping is golden brown, about 10 minutes.