Place a skillet over medium heat and add ½ cup water. As soon as you see bubbles, add one-third of the spinach and cook, stirring occasionally, until most of the spinach is wilted, then add more. Continue to cook, stirring occasionally, until all the spinach is in the pan and wilted, 6–8 minutes. Transfer spinach to a bowl of ice water to stop the cooking and lock in its bright green color. Drain and squeeze out excess liquid. Finely chop spinach and set aside.