Turkey and cranberry is the Christmas-leftover sandwich defined by its sauce, and the sauce is sweet-tart fruit rather than anything savoury. Cold roast turkey goes onto bread with a spoonful of cranberry sauce, and that single sharp, jammy, faintly bitter condiment is what names the sandwich and what makes it work. The turkey on its own is the same lean, cooled, slightly dry meat any turkey sandwich struggles with; the cranberry is the decision that defines this build, a bright acid-and-sugar note that cuts the flatness of cold breast and supplies the lift the gravy gave the bird on the plate the day before. Without it this is just cold turkey on bread. With it, it is the sandwich the rest of the year remembers Christmas by.
The craft is the balance between a wet, sweet sauce and a dry, mild meat. Cranberry sauce is sharp and sugary and loose, so it is spread in a measured stripe rather than a flood, enough to carry every bite without the sweetness taking the sandwich over or the liquid soaking straight through the crumb. The turkey is sliced thin and against the grain and laid loose rather than packed tight, because dense layers of a dry meat read drier still and a thin slice takes the sauce more evenly. Butter to the edges does its usual structural work and also functions as a barrier the other way, keeping the wet sauce off the crumb while still bridging the meat to the bread. The bread can be softer than a beef sandwich would take, a plain white or a light wholemeal, because there is no heavy fat to fight and the priority is a yielding mouthful around a sauce that is doing the lifting.
The variations are the rest of the Christmas table folded in around the same fruit-and-bird core. Adding sage-and-onion stuffing turns it into the fuller leftover sandwich and shifts the lead from sweet to savoury; a smear of bread sauce brings a milky, peppery softness; a leaf of rocket or watercress adds a peppery counter to the sweetness; brie melted against the warm turkey pushes it richer. The savoury stuffing-led reading is a distinct sandwich with its own logic. Each deserves its own article rather than being crowded in here.