Instructions

1.  

2. Preheat oven to 350°F with rack 10 inches from heat. Bring a large saucepan of water to a boil over high. Add 1 tablespoon salt and stir in shells; cook according to package directions for al dente. Drain shells and transfer to a large bowl. Add 1 tablespoon oil; toss to coat. Set cooked shells aside.

3. Wipe saucepan clean. Add butter and melt over medium. Whisk in flour; cook, whisking constantly, until mixture is lightly browned, 3 to 4 minutes. Gradually whisk in half-and-half and milk until sauce is smooth. Bring just to a simmer over medium-high, whisking occasionally. Reduce heat to low; simmer, whisking often, until no floury taste remains, about 5 minutes. Remove from heat. Gradually whisk in 1 1/2 cups Fontina and 1 1/2 cups cheddar until smooth. Whisk in onion powder, garlic powder, white pepper, and nutmeg. Fold in cooked shells. Season with 1 1/2 teaspoons salt and the black pepper. Spread mixture evenly in a 2-quart broiler-safe baking dish. Sprinkle with remaining 1/2 cup Fontina and remaining 1/2 cup cheddar.

4. Bake in preheated oven until bubbling around edges, about 20 minutes. Increase oven temperature to broil. (Do not remove baking dish from oven.) Broil until browned in spots, 3 to 4 minutes. Remove from oven; let cool 5 minutes.

5. Meanwhile, heat remaining 2 tablespoons oil in a medium skillet over medium. Add panko; cook, stirring constantly, until deep golden, about 4 minutes. Transfer to a medium bowl and let cool 2 minutes. Stir in parsley, lemon peel, and garlic. Season with remaining 1/4 teaspoon salt. Serve gremolata breadcrumbs with shells.