Throwing Away A Win

BENIDORM U2000, along with its sister tournament, which is for players rated under 2301, is unusual in that it consists of 10 rounds over nine days (some years, but not very often, it is 10 rounds over 10 days).
Each round starts at 4.30pm, except for the double-round day when the morning game begins at 10am.
Yesterday saw this year's double-round day, but my morning opponent did not turn up (an all-too-frequent occurrence in Spanish tournaments in my experience), so I had to sit around twiddling my thumbs for an hour in case he showed.
In the afternoon/evening round, I reached the following position against an 11-year-old boy.

White to make his 40th move in Spanton (1940) - Pablo Fuertes Cirauqui (1807)

*****
*****
*****
*****
*****
*****
40.e6??
White's advantage is overwhelming, but this is not the way to convert it.
If I had been taking my time, I would have seen the danger to my king from a check on h6.
Stockfish9 reckons it is mate in 29(!) moves starting with 40.g4. In any event, I needed to give my king more air.
40...Bh6+ 41.Ke5 Re3+ 42.Kd4 Rxe6 43.Qd8+ Bf8
I could see no way to make progress and so felt obliged to accept my opponent's draw offer (made in my time, naturally).