1. Cook macaroni according to package directions. Meanwhile, in a large saucepan, melt butter over medium heat.
2. Stir in flour, salt and pepper until smooth; gradually whisk in milk. Bring to a boil, stirring constantly; cook and stir 1-2 minutes longer or until thickened.
3. Stir in cheese until melted.
4. Drain macaroni; add cheese sauce and stir to coat. If desired, sprinkle with cayenne pepper.
For the Sandwich
1.Over medium heat in nonstick skillet, fry bacon. Remove from pan and place on paper towel-lined plate.
2. In same skillet, warm macaroni and cheese in bacon grease. Once warm (about 3-4 minutes), shape mac & cheese into two squares, each about the size of the bread and top each with slice of cheese. Remove from heat.
3. Butter 2 slices of bread and place both slices, butter-side down, in another skillet over medium heat.
4. Top one of the bread slices with cheese slice. Place two slices of bacon on top of the cheese. Use spatula to transfer one mac & cheese square onto cheese and bacon-covered bread in the skillet.
5. Cover with the other bread slice, toasted-side up. Gently press together with spatula and transfer to a plate. Repeat for second grilled cheese sandwich. Serve immediately.