Solution
First of all, thanks for the big interest and all your hard tries to solve my chess problem. The number of strong Steemit chess players who are taking part is increasing and thus it is becoming really hard work to reply to all your comments and suggestions! :)
Today I don't want to declare a winner. There are three people which will receive a 50 % upvote instead: @greatwolf and @jamesbrown for finding the most beautiful variation but also @juanmi96 for finding a solution in the most complicated variation finally.
Here now the solution:
1. a7 ('paralyzes' the black queen) Qc8 (Qa8 isn't better)
2. e5 (black must be prevented from playing e5 itself)
Now let's consider two black answers:
a)
2. ... c4 (with the idea c5 and Nc6)
3. Ng4 (idea: Nh6#) hxg4+
4. Kxg4 (white's king will slowly walk to h6 now, followed by Qg7#)
For example:
4. ... c3
5. Kg5 c2
6. Kh6 cxd1Q (c1Q+ or c1B+ only extend the game for one move)
7. Qg7# (checkmate)
b)
2. ... g5 (the toughest defence)
3. Qxg5+ (the only winning move) Bg6 (Kh8 loses even faster)
4. Qh6 (the only winning move which prevents Kh7) Bf5+
5. Kh2 Bg4 (After 5. ... Bg6 white plays 6. Rg1 and then 7. Ne4)
6. Nxg4 hxg4
7. Rg1 f5
8. exf6+ (remember the en passant rule!) Rxf6
9. Rxg4+ Rg6
10. Rxg6+ Kf7
11. Qg7# (checkmate)
You created a really fantastic chess riddle based on the idea of GM Nigel Short in his famous game against Jan Timman!
I can't believe that I didn't even consider Qxg5+ in response to g5...well, I think I did for like a second, but gave up on it for some reason....hmm, lol.
Thanks for providing these chess puzzles @jaki01. It's a nice way to wake up the brain cells in the early morning.
I am happy to read that you like my riddles! :)
Danke