A nasty problem

I was browsing through my copy of Karsten Muller & Frank Lamprecht's Fundamental Chess Endings a couple of days ago and opened it up to the following exercise, which they give ***** ("extremely difficult"):

V. Halberstadt, 1938

White to play and win

4N3/3nP3/1k6/8/1K6/8/8/8 w - - 0 1

The solution in the back identifies this as a study by V. Halberstadt, and that it shared the first & second prize in 1938 in Gros. No idea what Gros was or is, possibly a magazine? Anyhow, I found it to be an entertaining puzzle, and while I eventually worked out what the first move had to be, I couldn't work my way to the solution.

I'll post the solution in a week or so*. In the meantime, happy hunting!

* A reasonably good program should find the answer quickly, for those that can't wait.