Butter both sides of all 8 bread slices generously. Heat a skillet over medium-high heat for 2 minutes until it's hot enough that water droplets dance across the surface. Toast each slice 1-2 minutes per side until golden brown and crispy, working in batches if needed.

While bread toasts, combine mayonnaise and Dijon mustard in a small bowl with a fork. Stir until completely blended and smooth. This creamy base spreads easily and adds richness without overpowering other flavors in your sandwich.

Warm your sliced leftover turkey in a small saucepan with the gravy over medium heat. Stir occasionally for 3-4 minutes until the turkey reaches 165°F internally and steams gently. Never let this bubble aggressively or your meat becomes tough and stringy.

Assemble your thanksgiving leftover turkey sandwich family recipe by spreading the mayo-mustard mixture on four toast slices. Layer lettuce, then tomato slices, then red onion rings across each prepared base. This order prevents moisture from making bread soggy too quickly.

Top lettuce with warm gravy-coated turkey slices, dividing evenly among all four sandwiches. Sprinkle cheddar cheese over the warm meat so it softens slightly from residual heat. Add 1/4 cup warm stuffing to each sandwich for textural contrast and nostalgic flavor.

Complete assembly by placing remaining toasted bread slices on top, mayo-mustard side down. Press gently so everything adheres without squishing delicate ingredients. Season the outside with salt and pepper if desired.

Slice each sandwich diagonally if serving to younger children—they find this presentation more appealing. Transfer immediately to serving plates and enjoy while bread remains warm and crispy. The combination of textures deteriorates within 5 minutes if left sitting.