Steaming the leafy vegetable needs to be done without any water, while the whole leaves can be sauteed in butter.
In this way, the carotene and healthy vitamin C are retained and absorbed better. Boiling needs to take place in a tightly closed container. The maximum amount of time for boiling is between 10 - 15 min.
For the healthiest possible preparation, cook the spinach by steaming. Place the leaves atop a cooking grid or in a gauze bag.
If you blend or mash the spinach, you "kill" a large amount of the vitamin C content. This is because this type of treatment destroys the wholeness of the cells, while the oxygen in the air in the room ruins the substance.
Experts recommend sauteing the whole leaves in oil as the best method of preparation. Simply apply a few drops of oil to the pan, put in the spinach leaves, then cover with a lid.