Remove the mac and cheese meatloaf slice from the refrigerator and allow it to rest at room temperature for about 5 minutes so it reheats evenly.

Heat a skillet over medium-low heat and add a small amount of butter or oil to lightly coat the surface.

Place the meatloaf slice in the skillet and heat gently for 3 to 4 minutes on the first side, allowing the bottom to warm without browning too quickly.

Flip the slice carefully using a spatula and continue heating for another 3 to 4 minutes until warmed through and the macaroni layer softens.

If using sliced cheese, place it directly on top of the meatloaf slice during the last minute of heating so it melts slightly.

Remove the heated meatloaf slice from the skillet and set aside briefly on a plate.

Wipe the skillet clean if needed, then return it to medium heat.

Butter one side of each bread slice and place them butter-side down in the skillet.

Toast the bread for 1 to 2 minutes per side until golden and lightly crisp, then remove from the skillet.

Spread mayonnaise or sandwich spread on the untoasted side of one bread slice if desired.

Place the warm mac and cheese meatloaf slice on top of the spread, keeping it centered for even bites.

Top with the second slice of bread, toasted side facing outward.

Press gently on the sandwich to help it hold together without compressing the filling.

Transfer to a cutting board and slice in half for easier eating.

Serve immediately while warm for best texture and flavor.