一揮而就 [－挥－－]

Jyutping jat1 fai1 ji4 zau6
Pinyin yī huī ér jiù

Definitions (CC-CEDICT)
  1. to finish (a letter, a painting) at a stroke
Definitions (Wiktionary)
  1. phrase, idiomatic
    a flourish of the pen and it's done; to finish a piece of writing or a painting at one go