I tried looking for the book’s pdf I used to study from but I couldn’t find it, some time has passed. If I am not mistaken the book was “Conditions of Nervous Anxiety and Their Treatment”. It’s a book which contains a lot of stuff but if I recall correctly there was a chapter on stuttering. Also, still if I remember correctly, he reports analysis of patients in said book. Idk if that’s the definition of “applied psychology” but you could give it a look