I think it’s really important to wash the spinach – it doesn’t matter what it says on the package! You will find that it’s not really clean. Spinach is grown in sandy soil that is well drained. That means there is going to sand someplace in the package. So please wash it before you begin.
Fill a sink with lots of cold water and throw in the spinach – move it around a bit and let any sand in it sink to the bottom of the sink. Lift hand fulls of spinach out of the water letting it drain back into the sink. Then spin it dry or dry in a towel or with paper towels.
Color: Using fresh spinach is the way to get that great bright green color. You can use frozen spinach if you like and it will taste fine but won’t have the color.
You don’t need to simmer it for more than 15 minutes! If you do you will lose the color and it will darken.
The potatoes are there to use as a natural thickener and you won’t really taste them.
If you use frozen spinach be sure to squeeze out the water, then add to the pot.
Refrigerate it as soon as it cools enough to handle to help it keep it color.