Cauliflower and Horseradish Gratin

Recipe courtesy of wrysmyguy

• 3 1/2 pounds cauliflower, trimmed, cut into florets (about 8 cups) 
• 6 tablespoons unsalted butter 
• 3 tablespoons all purpose flour 
• 2 cups half and half 
• 7 tablespoons prepared white horseradish 
• 1 teaspoon white wine vinegar 
• Ground nutmeg 
• 1 cup packed grated Fontina cheese (about 4 ounces) 
• 1/2 tablespoon Dijon mustard 
• 2 cups fresh French breadcrumbs 

Preheat oven to 375***176;F. Steam cauliflower until crisp-tender, about 9 minutes. Transfer to 13x9x2-inch glass baking dish. Melt 3 tablespoons butter in heavy large saucepan over medium heat. Add flour and stir 2 minutes (do not brown). Gradually whisk in half and half. Cook until sauce boils and thickens, whisking constantly, about 4 minutes. Mix in 5 tablespoons horseradish and vinegar. Season to taste with nutmeg, salt and pepper. Pour sauce over cauliflower and mix to coat. Sprinkle cheese over. (Can be made 1 day ahead. Cover and chill.)
Melt 3 tablespoons butter in heavy medium skillet over medium heat. Mix in mustard and remaining 2 tablespoons horseradish. Add breadcrumbs; stir until crumbs are golden brown, about 9 minutes. Sprinkle over cauliflower.
Bake until cauliflower is heated through, about 25 minutes.

Serves 8 to 10.