A case in point is a piece she wrote in 1992 called A Southern Gothic Childhood, With Codeine. Originally published by Harper's magazine as a memoir, it later turned up in The Penguin Book of New American Voices renamed Sleepytown and rebranded as fiction.
When I start to ask about this, Tartt, quite narked, cuts in. ''That is a short story. It is a short story. It's a short story. I was very upset when it appeared in Harper's with the designation 'memoir'. It's a short story. It's a short story.''
So it's largely untrue then? Typically, she shields herself from this straight question with a literary reference, directing me to the similarities between the short story collection Nabokov's Dozen and his autobiography Speak, Memory. ''If you are reading his autobiography you see very clear elements of these stories of Russian childhood,'' she concludes. ''But, you know, he chooses to call them stories. And Sleepytown is a story. I'm glad you asked me that. I'm glad to clear that up.''
Tartt, who veers between a politely dogged reticence and sudden outbursts of candor when discussing her childhood, bridles when I raise the subject of A Southern Gothic Childhood. It was written as a short story, she insists, not a memoir "and I was shocked when it came out in that way" - although, she adds, "it's true about the codeine".
TARTT attended Miss Doty's Kindergarten For Girls where, at the graduation ceremony, she announced her intention to become an archaeologist. She had a taste for boy's-own adventure. Her heroes were Harry Houdini and Robert Scott. Female role models were thinner on the ground, though the androgynous Joan of Arc was certainly one.
Set in 1970s Mississippi, The Little Friend stars an engagingly cranky 12-year-old girl who is like a caricature of her creator's gloomy, bookish youth.
Tartt easily imagined herself back into a pre-pubescent mind with the help of childhood notebooks in which she kept diaries, fiction, drawings and collages. In a 1992 essay, she wrote about her "skittish, immature mother" and "dashing but feckless father" and the bevy of great-aunts and grandfathers who brought her up. From a baby so small she wore doll clothes, she grew into a sickly child dosed on whiskey and cough syrup by her great-grandfather. "I spent nearly two years of my childhood submerged in a pretty powerfully altered state of consciousness ... I was convinced that I would die soon."
The elder of two daughters, Tartt was brought up in "shabby gentility", in a big house "filled with beautiful things and lots of books". Her family on her mother's side, the Boushés, were "old South", which is to say they had lived in Grenada for about as long as the town had existed.
Her mother Taylor worked as an executive with the State Employment Commission. Her father Don was a wild card, an erstwhile rockabilly musician who somehow metamorphosed into a local politician of some substance, and was seldom seen at home.
Don Tartt was an upwardly mobile small-town operator who went from working in a grocery store to owning a freeway service station to becoming a successful local politician. At one point he was president of the Grenada County Board of Supervisors. He and his wife, Taylor, a secretary for much of the time they were married, stayed together for two decades - on the evidence, not happy ones. They produced two daughters; the elder showed unsettling signs of precocity.
Much of Tartt's childhood was spent surrounded by an extended family of sundry aunts, grandparents and great-grandparents. Her parents are now divorced, and she has not spoken to her father in years.
Books were "the great escape". Books were about "being somewhere else". Above all, she was "a girl who loved books for boys". Ivanhoe, Jules Verne, James Fennimore Cooper, Robert Louis Stevenson. A favorite childhood game was enlisting her less literary-minded friends to enact scenes from Kidnapped. (Harriett, by the by, does much the same thing.) "And," adds Tartt, "I loved, LOVED Peter Pan." By the age of 12 she was working her way through Dickens and Kipling. This enamoration with 19th-century literature and its tradition of storytelling - the almost total absence of any influence that might be described as "modern" - seems essential to understanding Donna Tartt.
The old joke in Mississippi is that there are more writers than there are people who know how to read. At 13 Tartt was publishing poetry in the Mississippi Literary Review. She would compete for any literary prize to hand, and invariably win it. In 1981 she arrived at the University of Mississippi at Oxford, which is known as "Ole Miss".
This evasiveness about her childhood is a surprise, because in 1992 - perhaps before she realised how big her celebrity would become - she wrote a beautiful, and very intimate, memoir of the time for Harper's magazine. It presents the story of a bizarre childhood. She was, she wrote, "too small to wear regular baby clothes", so was instead dressed in doll's clothes. "There exists a hilarious photograph of me lying in a crib and wearing, for an infant, an oddly sophisticated career-girl outfit," she writes. She describes how her great-grandfather, the great patriarch of her family, "had a nearly unlimited faith in the magic of pharmacy" and has spent the last years of his life constantly dosed up with antibiotics, "believing them to be a kind of healthful preventative, or nerve tonic".
At an age when most girls her age were reading Misty of Chincoteague, Donna Tartt idolized Heinrich Schliemann, genius linguist and excavator of Troy. "When I was little," she says, "my grandmother gave me this book about archaeology, which was my favorite thing in the world. It was not a child's book. When I graduated from high school, one of the girls I had been in kindergarten with had brought a tape recorder to our kindergarten graduation. At Miss Doty's Kindergarten for Girls. They made us all stand and say what we wanted to be when we grew up. And when it was my turn, it was exactly my voice, except it was much higher-pitched. And I said, 'My name is Donna Louise Tartt, and when I grow up, I should like to be an ar-chae-ologist.' I was the only child that said should - all the other children said would. It was starting even then. Child is father to the man."
She wrote her first poem at age five, lying on her stomach in front of the TV; she had to wait eight more years to be published, with a sonnet in a Mississippi literary review. By the time she was in high school, she was churning out the words in a promiscuous frenzy, winning prizes for her essays on patriotism and the dangers of alcohol, writing short stories about death. Then came college.
So the first thing I wanted to know when we met was just how much of Tartt was in Harriet. "Not as much as you might think," she replies. Yes, both Harriet and Tartt grew up in small Mississippi towns in the '70s. Both were loners, voracious readers with few playmates and surrounded by aging relatives. "Harriet is actually more a state of mind, a sort of no-nonsense trait that runs in my mother's side of the family. My great-grandfather used to talk about his own grandmother like that, and she must have been born in the 1820s or 1830s." And frankly, Tartt is much nicer, and a lot funnier, than the grimly determined little girl in this novel. You can't imagine Donna Tartt trying to kill anyone, certainly not with a cobra.
So great was her love for Stevenson that she used to press-gang the neighbourhood kids into dramatizing passages from Kidnapped. ''I used to try to,'' she says, ''but I didn't know other children who read, really. Most of the other children I knew watched television, and reading was something that happened inside my family.
''I could be a very bossy little girl, and instead of playing tag or something like that, I used to stage manage everybody into this game, which was Kidnapped. No one else realized what it was, but we all had a good time. The storming of the round-house, you know that scene? I was ritually acting the book out in some way, which is funny to think about.''
At five, Tartt wrote her first poem. Eight years later, she was published for the first time, by a local literary journal. Does she remember what that felt like?
''A-mazing! Amazing. The first thing I had in print was a poem. I was so proud. Actually I showed it to my English teacher, I was so proud. Because it's not the sort of thing you want to show your friends. It's a little bit uncool. It was a sonnet. Yeah, I showed it to my mother, and I showed it to my English teacher. And she had the school make an announcement over the public announcement system. As we were sitting in the classroom, the Principal was going: 'We have a published poet in our school.'
''But it was actually very funny because boys who would never talk to me before were going 'You published something? They printed something you wrote? What was it?' They were interested. It was interesting because it was so strange. Like one of us being on television or throwing out the leading ball in a Major League game or just some strange fact.''
Tartt's mother, by contrast, was described to me by someone who's met her as "a Blanche DuBois figure who said things like 'the south is a defeated nation'." Tartt says about her: "She's funny as hell and I talk to her on the phone every day. She's a big ole southern belle - very over-the-top, in a funny and good way. She's very campy."
Tartt got her own start in sleepy Grenada, Mississippi, where her adored mother worked as an executive with the State Employment Commission, and her father was a local politician. Back then Tartt, the elder of two daughters, pictured herself as a writer - or "an archeologist with a big hat tromping around the Pyramids." Or a painter, or a dancer.
"I don't think it ever entered my mother's head that we would earn livings," the novelist laughs. "She's perfectly happy for us to do whatever we like and stay at home." Tartt ended up writing much of "The Secret History" there, the rest while shuttling among "country houses belonging to a variety of people," and the modest Greenwich Village apartment she shares with a cockatiel, Horace, and a pug named Pongo.
Here's Donna at Kirk Academy: "I was in high school no more than three days a week and usually I didn't stay the whole day," she begins. "I would go into the office and say to the receptionist," - here the drawl thickens dramatically - "'Miss Betty, I don't feel well, I'd like to call my mother to come pick me up.' . . . At home I'd make some lunch, get in bed with it and read. That's still my greatest luxury - to stay at home in bed and read. . . . I'd rather spend the rest of my life reading," she says, "than ever write another book."