One-of-a-kind: unique: one that does not exist elsewhere.
ユニークな、比類のない、他にない

Tom: Have you tried this new chocolate? It's truly one-of-a-kind
Noriko: No I haven't. That's the one from Switzerland, isn't it?

トム：この新しいチョコレート試してみた？これ、本当に独特だよ
ノリコ：まだ試してないわ。それってスイスのでしょ？