Oh guys – in northern Europe, for cookbooks to sell they have to be very precise (the same is true in the USA). I wish that I had a pound for every time I have typed " Heat the oil in a frying pan, add the onion and cook over a low heat, stirring occasionally, for 5 minutes, until softened.' Nearly 40 years of doing that – I'd be a rich woman.
Southern European cookbooks are quite different. "Make a Béchamel sauce (without even giving a quantity or list of ingredients, let alone a method). "Cook until ready" – no idea whether it is designed take 10 minutes, 30 minutes, 1 or 2 hours. Often no oven temperatures, no cooking times. It's easy to go off piste with Brit cookbooks because there's already lots of guidance, aπd so, of course, you should, if you want to – but it's quite different if you're dealing with continental ones.