Butternut Squash Mac and Cheese

Ingredients

• One 2- to 2 3/4 pound (960g) butternut squash, halved and seeded
• 1 tablespoon (15ml) extra-virgin olive oil
• 1 3/4 teaspoon Diamond Crystal kosher salt, divided; for table salt, use half as much by volume
• 4 medium garlic cloves (20g), peeled and smashed
• 1 pound (454g) medium-size pasta shells or other short pasta
• 6 tablespoons unsalted butter (about 3 ounces; 84g), divided, plus more for greasing
• 1/4 cup all-purpose flour (about 1 ounce; 32g)
• 1 teaspoon paprika
• 1/2 teaspoon freshly ground black pepper
• 1/4 teaspoon ground nutmeg
• 2 1/2 cups (590ml) whole milk
• 1 1/2 cups (355ml) half-and-half
• 1 1/2 tablespoons Dijon mustard
• 12 ounces fontina cheese (340g; about 3 cups), shredded
• 12 ounces extra-sharp cheddar (340g; about 3 cups), shredded
• 8 ounces Gruyère cheese (226g; about 2 cups), shredded
• 1 cup panko breadcrumbs (2 1/2 ounces.; 71g)
• 1 tablespoon minced fresh sage

Instructions

1. Adjust oven rack to middle position and preheat oven to 400°F (205ºC). Line a 13- by 18-inch rimmed baking sheet with foil or parchment. Set aside.
2. Rub oil and 1/2 teaspoon of the salt all over cut sides of butternut squash. Place two smashed garlic cloves in each squash cavity and place squash halves cut side down on prepared baking sheet. Bake until easily pierced with a fork, 30 to 40 minutes. Remove from oven and let cool slightly, about 5 minutes. Reduce oven temperature to 350°F (175ºC) and, using oven mitts, carefully move rack to top third position.
3. While butternut squash bakes, bring a large pot of lightly salted water to a boil. Add pasta and cook, stirring, until just shy of al dente, about 2 minutes less than cooking time indicated on package. Drain pasta and set aside.
4. In the now-empty pot, melt 4 tablespoons butter over medium heat. Once melted, add flour, paprika, pepper, and nutmeg, and whisk to form a paste. Continue to cook, whisking constantly, until raw flour scent is gone, about 1 minute. In a 4-cup measuring cup, combine whole milk and half-and-half. Slowly pour milk and half-and-half in a thin, steady stream, whisking constantly and thoroughly and getting into all corners of the saucepan to maintain a homogeneous texture. Sauce will initially become very thick, then get very thin once all the milk is added. Whisk in Dijon to combine.
5. Scoop out roasted squash flesh (about 3 to 4 cups) and garlic and add to milk mixture in pot. Using an immersion blender, blend squashand garlic into milk mixture until smooth (alternatively, combine squash flesh, garlic, and 2 cups of the milk mixture in a blender; blend until smooth. Stir back to saucepan); bring to a simmer over medium heat. Remove from heat and gradually whisk in fontina and cheddar, about 1/2 cup at a time, until smooth and creamy, 5 to 7 minutes.
6. Fold in cooked pasta to fully coat in sauce, followed by Gruyère and 1 teaspoon salt. Lightly grease a 9- by 13-inch baking dish with butter and scrape pasta mixture into prepared dish and smooth surface into an even layer.
7. Microwave remaining 2 tablespoons butter in a medium microwave-safe bowl on low power until melted, about 20 seconds on medium power. Add panko, sage, and remaining 1/4 teaspoon salt, stirring to evenly coat breadcrumb mixture in butter. Scatter panko all over surface of mac and cheese in an even layer. Place baking dish on a 13- by 18-inch rimmed baking sheet and bake at 350ºF on upper-middle rack until browned and bubbling, 35 to 40 minutes. (Ovens can vary; check often to prevent top from burning.)
8. Remove from oven and let cool for 15 minutes. Serve.