How to write "BiángBiáng麵" using pinyin?
Phonetic Substitution

Although the character cannot currently be typed into a computer, wikipedia notes that one may use a phonetic substitution. I doubt that most people would recognise this 58 stroke original character in any case but at least this may be a usable substitute.


  The Chinese character for "biáng" cannot be entered into computers.
  Therefore phonetic substitutes like Chinese: 彪彪面; pinyin: biāobiāo
  miàn) or Chinese: 冰冰面; pinyin: bīngbīng miàn) are often used.


(Wikipedia, n.d., https://en.wikipedia.org/wiki/Biángbiáng_noodles#Mnemonics)