The Veda sandwich is one of the small set of sandwiches where the bread is the entire subject, and in Northern Ireland that bread is Veda: a dark, soft, malted loaf, faintly sweet and slightly sticky in the crumb, with a flavour closer to a malt loaf than to a plain sliced white. The sandwich is built to present it. Two slices of Veda, butter, and very little else, because the loaf already carries a malty depth and a tacky, tender texture that a strong filling would only bury. This is not bread chosen as a neutral carrier for something more interesting; it is the interesting part, and the build is an exercise in staying out of its way.
The craft is restraint and the handling of a soft, sweetish, slightly damp crumb. Veda is tender and a little sticky, so it does not want a heavy, wet filling that would compound the moisture already in the loaf and turn it gluey; a thin scrape of cold butter against the malt is the classic reading, the salt of the butter setting off the loaf's faint sweetness the way it does on a malt loaf. Toasting is the other standard move, and it changes the sandwich rather than just warming it: heat caramelises the malt sugars at the surface, firms the tacky crumb into something with a little crispness, and pushes the loaf's flavour forward, which is why a Veda is so often eaten toasted with butter melting into it rather than cold. Either way the filling stays minimal because the point is the bread.
The variations stay deliberately close to the loaf. Toasted Veda with butter is the everyday form; a slice of a strong Cheddar against the malt is the most common addition, sweet bread set against sharp cheese; jam or marmalade leans into the loaf's own sweetness for a near-cake reading; a savoury filling such as bacon treats the malt as a sweet counter to salt. Each deserves its own article rather than being crowded in here.