The chocolate-spread sandwich is the made thing rather than the jar: chocolate spread taken out of the cupboard, dragged across soft white bread, closed, sometimes cut into triangles, and packed into a child's lunchbox or handed over at tea. The defining fact of this build is that it is assembled hours before it is eaten and has to survive the wait, which makes it a sandwich about endurance more than about flavour. It is the sweet sandwich a parent makes when there is nothing else and a child will reliably eat, and its quality is measured less by how good it tastes fresh than by whether it is still a sandwich at lunchtime rather than a sealed slice with a brown smear inside.
The craft is the spread, the bread and the proportion between them, because there is nothing else in it. The layer goes on thin, not because thin tastes better in the abstract but because a thick one is cloying, slides under the top slice, and squeezes out of the edges when the sandwich is pressed flat in a box. The fat in the spread is what makes the whole thing work as a packed lunch: it sits on the crumb rather than soaking through it the way jam does, so a chocolate-spread sandwich made at half seven is still intact at half twelve where a jam one would be a damp casualty. Butter underneath is the dividing question. Some build it spread on bare bread for an even sweeter result; others butter first, both to add the salt that stops the sweetness reading flat and to waterproof the crumb against what little oil migrates. The bread is soft plain white because the filling has no texture of its own and a chewy crust would be the only thing in the sandwich resisting a bite, which children notice and reject.
The variations are the small additions that fix the one-note softness or are negotiated at the point of making. Banana sliced in is the most common, adding a fruit note at the cost of a shorter life in the box. A scatter of hundreds and thousands turns the everyday version into a birthday one; peanut butter on the far slice adds the salt and body the spread lacks. The jar itself, considered as a filling rather than the finished sandwich, is its own subject. Each deserves its own article rather than being crowded in here.