Wash the spinach well, shred it coarsely, and heat it in a pot with just the water that sticks to the leaves. Add a pinch of salt and stir it until it is completely wilted (5 minutes), then let it cool and squeeze it well to remove all the moisture you can. Blend the spinach and combine it with the other ingredients when you make the dough. As variations, you can also use wild greens, or nettles (use gloves when you pick and wash them).