Does he?
His
basic risotto recipe states 15 minutes of 'cooking' time once the stock has started to be added, so let's be generous and say that can stretch to 20 minutes.
So I'm obviously missing something, as the only Jamie Oliver risotto recipe I can find that he thinks takes longer than 20 minutes to cook once the stock has been added is his
grilled mushroom risotto.
I don't see where the doubling of time comes from, especially given his recipes mainly revolve around 400g of rice. Sure, he talks about using 2 pints of stock, but that's a moveable feast as far as I'm concerned - stock cubes always need more liquid, fresh stock needs less.
Where did you find this recipe that takes 40 minutes? In one of his books?