Pick over the spinach carefully and wash it in at least 5 waters.
Break off the stalks and at the same time pull off the central ribs if coarse.
(Young, summer spinach need not be stripped of the central ribs.) Put the wet leaves into a saucepan, without additional water.
Cook slowly until tender, about 15 min., stirring the spinach in the pan occasionally.
The pan should have a tightly-fitting lid.
Drain well, pressing out the water.
Reheat in the butter.
Add the cream, if used, and mix it well with the spinach.
Season and serve hot.