March 30, 2019
To make the mac ’n’ cheese: Bring a medium saucepan of generously salted water (so it tastes like seawater) to a boil over high heat. Add the pasta and stir immediately. Boil the pasta, stirring occasionally, just until al dente, 8 to 10 minutes or according to the package directions (the pasta should be tender but still chewy, not mushy). Drain the pasta in a colander and set aside.
Put the empty pasta pan (no need to wash it) over low heat and add the butter. When the butter is melted, whisk in the flour mixture. Cook, whisking often, until the mixture is beginning to brown and has a pleasant, nutty aroma, about 1 minute. Watch carefully so it does not burn.
Slowly whisk the milk and cream into the butter-flour mixture, combining well. Cook, whisking constantly, until the sauce is heated through and just begins to thicken, about 2 minutes. Remove from the heat. Add the cheese gradually while stirring constantly in one direction with a wooden spoon or silicone spatula. Stir until the cheese has melted into the sauce, then stir in the cooked pasta.
Line a 9-by-13-inch rimmed baking sheet with parchment paper (or aluminum foil, in a pinch). Coat the parchment paper with nonstick cooking spray, then pour the warm mac ’n’ cheese into the prepared baking sheet and spread evenly with a spatula. Coat another piece of parchment paper with cooking spray and place, oiled-side down, directly on the surface of the mac ’n’ cheese. Refrigerate until cool and firm, about 1 hour.
Remove the mac ’n’ cheese from the refrigerator and peel off the top layer of parchment paper. Carefully cut into eight equal pieces. Spread 3/4 tsp of the garlic butter on one side of each bread slice. Place half of the slices, buttered-side down, on a clean cutting board. Top each with one slice of Cheddar, then one piece of the mac ’n’ cheese. (Transfer from the baking sheet by scooting your hand or a spatula under each piece of mac ’n’ cheese and then flipping it over onto a sandwich.) Place one slice of Jack on top of each. Finish with the remaining bread slices, buttered-side up.
Using a wide spatula, place as many sandwiches in the pan as will fit without crowding, cover and cook until the bottoms are nicely browned, about 4 minutes. Turn and cook until the second sides are browned, the cheese is melted, and the mac ’n’ cheese is heated through, about 4 minutes longer. Cut the sandwiches in half, if desired, and serve. Repeat to cook the remaining sandwiches.