How to Make It
In a medium bowl, mix the flour with the salt. Add the water and 1 tablespoon of the olive oil and stir with a wooden spoon until a dry, shaggy dough forms. Turn the dough out onto a work surface and knead until smooth, about 5 minutes. Quarter the dough and roll each piece into a ball. Cover the balls with a damp paper towel and plastic wrap and let stand for 30 minutes.
In a medium skillet, melt the butter over moderate heat. Add the onion and garlic, increase the heat to moderately high and cook until softened. Add the spinach, crushed red pepper and nutmeg and cook, stirring, until the spinach wilts, 2 to 3 minutes. Add the flour and cook for 1 minute, then stir in the milk and cook until thickened. Remove from the heat. Fold the feta into the spinach mixture and season with salt and pepper.
On a work surface, roll out each ball of dough to a 6- to 7-inch round. Heat a large griddle. When it is hot, brush 1 side of a dough round with olive oil and transfer it to the griddle, oiled side down. Brush the dough with oil and cook over moderately high heat for about 2 minutes, until browned on the bottom. Turn the bread over and spread one fourth of the spinach mixture all over it. Cook until browned on the bottom, about 2 minutes longer. Transfer the bread to a work surface, roll it into a cone and serve right away. Repeat to make 3 more spinach flat breads.