Cook the spinach in a large saucepan over low heat with just the water that clings to it after washing. Cook until completely wilted. Squeeze out excess water.
Put the spinach in a large food processor and chop for ten seconds. Add all other ingredients, one at a time, except sour cream, salt and pepper. Puree. Add more cream if looser texture is desired. (Watch it: one time it got the texture of baby food when it was pureed too much, though it still tasted great.)
With a spatula, load the spinach into a butter-coated saucepan. Reheat slowly, stirring to prevent scorching. Remove from heat stir in sour cream. Season to taste.