1 1/2 tablespoons cornstarch
1 1/2 teaspoons dry mustard
1 1/2 teaspoons curry powder
2 1/4 cups whole milk
6 tablespoons (3/4 stick) butter
2 1/4 cups (packed) grated sharp cheddar cheese (about 10 ounces)
8 ounces small elbow macaroni, freshly cooked

2 1/2 cups fresh breadcrumbs made from 8 ounces trimmed sourdough bread

Preheat oven to 350 F. Butter 8 x 8 x 2-inch glass baking dish. Combine cornstarch, 1 teaspoon dry mustard and 1 teaspoon curry powder in heavy large saucepan. Gradually whisk in milk. Add 2 tablespoons butter. Whisk over medium-high heat until sauce thickens and boils, about 1 minute. Remove from heat. Add cheese and whisk until smooth. Mix in macaroni. Season with salt and pepper. Transfer to prepared baking dish.

Melt remaining 4 tablespoons butter in heavy large skillet over medium-high heat. Mix in remaining 1/2 teaspoon dry mustard and 1/2 teaspoon curry powder. Add breadcrumbs and stir until crumbs are crisp and golden, about 8 minutes.

Sprinkle crumb mixture over macaroni and cheese. Bake until warmed through and bubbling at edges, about 30 minutes. Serve hot.