Grilled Mac and Cheese Sandwich

Make the mac and cheese

1. Bring a medium saucepan of generously salted water (you want it to taste like seawater) to a boil. Add the pasta and cook, stirring occasionally, until al dente, 8 to 10 minutes, or according to the package directions. The pasta should be tender but still chewy. 2. While the pasta is cooking, in a small bowl, whisk together the flour, mustard powder, garlic powder, salt, black pepper, and cayenne pepper. 3. Drain the pasta in a colander. Place the empty pasta pan (no need to wash it) over low heat and add the butter. When the butter has melted, whisk in the flour mixture and continue to cook, whisking frequently, until the mixture is beginning to brown and has a pleasant, nutty aroma, about 1 minute. Watch carefully so it does not scorch on the bottom of the pan. 4. Slowly whisk the milk and cream into the flour mixture until everything is really well combined. Cook, whisking constantly, until the sauce is heated through and just begins to thicken, about 2 minutes. Remove from the heat. Gradually add the cheese while stirring constantly with a wooden spoon or silicone spatula and keep stirring until the cheese has melted into the sauce. Then stir in the drained cooked pasta. 5. Line a 9-by-13-inch (23-by-33-centimeter) rimmed baking sheet with parchment paper or aluminum foil. Coat the paper or foil with nonstick cooking spray or slick it with butter. Pour the warm mac and cheese onto the prepared baking sheet and spread it evenly with a spatula. Coat another piece of parchment paper with cooking spray or butter and place it, oiled or buttered side down, directly on the surface of the mac and cheese. Refrigerate until cool and firm, about 1 hour.