dash off sth or dash sth off
To write or draw something [e.g. letter, book] very quickly and without trying very hard. [Escrever ou desenhar alguma coisa (e.g. carta, livro) muito rápido e sem se esforçar muito.]
Ex.: His latest novel, already a bestseller, was dashed off in under three weeks. [Seu último romance, já um best-seller, foi escrito nas pressas em três semanas.]
UsingEnglish.com assim define:
Meaning: Do something quickly, especially writing. Example: He DASHED OFF the report in a couple of hours.