Like all green vegetables, spinach benefits from quick cooking that retains its colour and nutrients. To make the process as speedy as possible, some cooks recommend plunging the leaves into a big pot of boiling water -- but that, nutritionally, is not best practice. A common technique is to shove the spinach into a pot, clamp on the lid, and cook it at a high heat until it wilts -- but the advocates of boiling do not like this technique, claiming that it cooks the spinach unevenly and causes some of the leaves to stew for too long.
I tried cooking spinach in my steamer last night. But the process was too slow, I think. I prefer method two, above: wash the spinach, transfer the wet leaves to a colander, transfer them again to a pot, clamp on the lid, and put the pot on a high heat. After a minute or so, take off the lid; if the leaves are starting to wilt, you can stir the top ones into the boiling liquid below. Carry on stirring. All the leaves should be cooked in another minute or less. Drain.
I have read that spinach loses nutrients as it cools. Is that true? I hope not, because I often allow it to cool, squeeze out the liquid with my hands, and reheat the leaves gently with some butter, salt and pepper, and perhaps some nutmeg.
Or what I did last night: fried mushrooms and garlic, stirred in four bottled anchovies until they melted, and added the squeezed spinach and some cream. I then divided this sauce between two saucepans, adding to my portion four whizzed, dried chillis -- an excessive number, but that's what I like. We ate this sauce with penne.