。
The famous author wrote another bestseller.
Literal
Famous-author [topic-は] again bestseller-book [object-を] write-[past-した].
著す ('to write, compose, author') is a formal/literary verb for authoring a book — more dignified than 書く. ベストセラー書 is a mixed compound with the loanword ベストセラー plus the suffix 書 ('book'). The combination feels a bit stilted but clearly communicates 'bestseller book.' Book-review or news-register.