Bring a large pot of water to a boil, salting it well (about 1 tablespoon) Add the spinach to the boiling water and cover the pot to return it to a boil. Uncover and boil the spinach until it wilts completely, about 1 min. Drain in a colander and hold the colander under cold running water to cool the spinach. Squeeze the spinach with your hands to remove excess water. (Don't worry about losing vitamins; you're mostly squeezing out water.) Chop the spinach coarsely (you should have about 1 cup); set aside.

In a large skillet over medium heat, melt the butter. Add the scallions and cook for 2 minutes, stirring occasionally. Add the chopped spinach, the cream, and the salt. Raise the heat to medium high. Cook, breaking up the spinach with a wooden spoon, until the spinach is tender and has absorbed most but not all of the cream and the pan is still a bit saucy, 3 to 5 minutes. Remove from the heat, season with black pepper, adjust the seasonings as needed, and serve.