Most amount of money made for least amount of time spent?

[ATV]

Might be a daft question, but does anyone know of a (legitimate) business model which generates the most amount of profit for the least amount of effort?

Probably any PHer who's doing really well is not going to spill his secrets all over a public forum but I'd like to ask the question and see if any ideas hit.

I did pretty well from the bitcoin surge in 2017 (bought in 2015) and was thinking of selling the coins and investing into another business (thereby deferring the CGT on them)

At the moment I'm on paternity leave and am casting about for ideas which won't require any demands on my time but that can bring serious return on an investment of £600k

Thanks