haha sorry to wreck your puzzle, but on move 5 if white played Kd3 instead of Qf1+? then black would have to play a1=N to prevent mate, and white could then play Kc3 and all black can do is stall a move with Nc2 Qxc2+ Ka1 Qb2 mate.
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I think best is 1. Kd3, which puts white's king in the mating square after queening his pawn a move before black, white can use the usual queen manuever to set up a mating net a little bit easier than in the puzzle.
Unless you've seen this before, its a tough one I think. I just made it up, but its useful in endings.
Don't forget to click the movelist. There are some variations in there that you may want answered.