Defrost the spinach, then press it out in a kitchen towel. Beat the egg whites until very stiff. Add a few drops of lemon juice and salt. Sift the cornflour over it and fold in carefully.
Add the spinach and mix gently with the beaten egg white. With 2 teaspoons, cut off small dumplings and put them into the hot (no longer boiling broth). Cover and let the dumplings simmer for about 5 minutes.
Makes about 12 dumplings.