Here's what I said about it yesterday:

I think Khakpour is intentionally developing a stammering, babbling narrative PoV in order to draw readers into her adaptation of an old Persian tale, so by using the "Khanoom" title/nickname in such a fashion, she is doing two things: defining the term for Anglo-Americans and showing how this character is a babbler. Such digressions are normal when we, especially when nervous, speak of the familiar to those who are strangers to it, so I think it adds to the narrative, instead of detracting.

As for the "exactly once," it's a play off of the Anglo-American fairy tale opening of "once upon a time," but inverting it by making it quite clear just how unusual this tale is in comparison to the standard fairy tale fare. As for "least visited whim," I suspect that's a purposely stilted way for an unusual character (I know a bit of his backstory now and let's just say that language, at least of the human variety, is not native to him) to explain why his mother didn't like conjugal sex. The "but a child like that, sure" references what comes in the paragraphs that follow the ones I quote: this is a very unusual-looking narrator and his childhood experiences even more so.

Perhaps with this knowledge, the prose takes on a different quality? It certainly is effective in setting up what follows after and that is why I quoted what I did, to see how the limited sample would appeal/not appeal to those who can't yet read the rest of the text.