Answer
  1. Nf6+!!

It's checkmate in 2 in one of two ways.

47...Qxf6
48. Qg4#

47...Kh4
48. Qh3#

https://www.chess.com/analysis/game/live/97535431411?tab=analysis

It's a speed chess game I just watched. Let me know if I screwed this up. I can't copy and paste from the site.

I was so fixated on how black was going to win - I didn't see the danger at all. I only knew black was toast due to the evaluation bar suddenly indicating mate in 2.

[Edit - I fixed a mistake]