Fisher & Donadson do the nicest regular butteries I’ve ever had.
the Condit Bakery in Inverbervie are the best I’ve tasted and always pick up a bag when i’m up that way.
As for what they are – Butteries – or “rowies” to the loons and quines of the Far North (east) are an ingenious form of self-buttering toast. Dating from the pre fridge days, Aberdeen fishermen would take them to sea. Eaten fresh, they’re fine, but as they go stale they’re better toasted. When you toast a stale one, the butter melts and presto! a self-buttering bread snack which tastes not completely unlike heavily buttered stale bread.