Grilled Mac and Cheese Sandwich

1. Make the mac and cheese: bring a medium saucepan of generously salted water to the boil, add the pasta, and cook, stirring occasionally, until al dente, 8 to 10 minutes.
2. While it cooks, whisk together the flour, mustard powder, garlic powder, salt, black pepper and cayenne in a small bowl.
3. Drain the pasta. Place the empty pan over low heat and add the butter; once melted, whisk in the flour mixture and cook, whisking frequently, until it begins to brown and smells nutty, about 1 minute, watching it doesn't scorch.
4. Slowly whisk in the milk and cream until well combined, then cook, whisking constantly, until heated through and just beginning to thicken, about 2 minutes. Off the heat, gradually add the cheese, stirring until melted into the sauce, then stir in the drained pasta.
5. Line a 9-by-13-inch rimmed baking sheet with greased parchment, pour in the mac and cheese, and spread evenly. Press another piece of greased parchment directly onto the surface and refrigerate until cool and firm, about 1 hour.
6. Make the sandwiches: heat a large cast-iron or non-stick skillet over medium-low heat. Stir together the 4 tbsp butter and garlic powder.
7. Peel the top parchment off the chilled mac and cheese and cut into 8 equal pieces. Spread three quarters of a tsp garlic butter on one side of each bread slice. Place half the slices buttered-side down, top each with a slice of Cheddar, a piece of mac and cheese, and a slice of Jack, then finish with the remaining bread, buttered-side up.
8. Griddle as many as fit without crowding, covered, until the bottoms are browned, about 4 minutes, then turn and cook until the second sides are browned and the cheese melted, about 4 minutes more. Repeat with the rest, cut in half if you like, and serve.

Tips from the ZestyPlate Kitchen

• Chill the mac and cheese until firm so it slices cleanly and stays put inside the sandwich.
• Griddle gently over a low heat so the bread crisps and the cheese melts before the crust catches.
• Brush the bread with garlic butter for extra flavour and a properly browned crust.
• Put a lid on the pan while it cooks to trap the heat and melt the cheese right through.