In the course of the past 15 years, and seemingly by accident, “The Great British Bake Off” has become one of the most popular shows on TV. In its best years, “Bake Off” has drawn more British viewers than “Downton Abbey,” “Sherlock,” and even Prince Phillip’s funeral. In the streaming era, “Bake Off” is the standard-setter for ambiently watchable TV; a generation of half-watchers turns to it for its gently sedative properties. Meanwhile, bakers watch it for the craft, thinking that maybe next year they’ll apply. Ruby Tandoh was one of those bakers. She sent in her application in early 2013, attaching photos of Viennese whirls, black-currant tarts, and a drum-size brioche à tête. At the very end of the audition process, Tandoh was sent to a psychotherapist, where she remembers crying for half the session, “constitutionally incapable of playing it cool.” That’s possibly why, Tandoh muses, a couple of months later, she was on the show. Tandoh takes us inside the tent and reflects o...