Pull away the centre ribs and wash the spinach in several lots of cold water. Lift the spinach dripping from the bowl and place straight in the saucepan. There will be sufficient water clinging to the leaves and no more will be required. Cover and cook over moderate heat for 5–10 minutes, shaking the pan occasionally.
Turn into a colander and press well to remove surplus water. Melt a nut of butter in the hot pan and return the spinach. Season to taste, toss gently in the butter and serve.