The first time Alison Bechdel wrote about her family was at college. She was doing "very, very badly" in an English class, and decided to write about a moment in childhood when she and her mother discussed the correct pronunciation of the word "ersatz". Both parents were English teachers, so the discussion of language was a given.
Her tutor loved the story. It turned around her standing on the course. "I think he thought I was a good writer," says Bechdel, "but actually I was just writing down what happened. I was not clever enough to make that up."
It was primarily transcription? "Yeah. I try to stick to that method as closely as possible".
She has used it for two family memoirs now, both highly literary, both told in cartoon form. That successful essay was the start of a life's work. The first memoir, Fun Home, focused on her relationship with her father, who died when she was 19, apparently killing himself after revelations about his sexuality, followed by the breakdown of his marriage. In 2006 Fun Home topped Time magazine's best books of the year and was declared a masterpiece.
Bechdel went from well-loved cartoonist – her comic strip Dykes To Watch Out For ran from 1983 to 2008 – to literary superstar. In her new memoir she moves on to her relationship with her mother, Helen, who is still alive, and therefore considerably trickier to write about.
There is an almost forensic quality to Bechdel's writing methods. She took to transcribing every phone conversation she had with her mother, for instance, without telling her. She pored over and copied out family letters, and delved through 40 years of her own diaries. Most strikingly, she took photograph after photograph of herself posing as her parents. These were used as a drawing aid, and are apparently pretty common for graphic novelists. But Bechdel accepts that the 4,000 photographs she took during the writing of Are You My Mother? might seem excessive. They served a bigger purpose, she says. "I do think it helps me to inhabit their characters, by assuming their physical position or manner. It gives me a kind of empathy, which I might not have if I weren't acting that out."
Bechdel, who is 51, lives in Vermont, and these photographs are kept in a computer file with all those of her daily life with her partner, artist Holly Rae Taylor. But the posed photographs far outnumber the others. Her life is her work, she says, "but my therapist is always trying to get me to let go of that idea, saying I need to have a life apart from writing. I'm trying to do that, but there's a great appeal in the possibility that your life could be a work of art."
Her memoirs are driven by an urge to fix or save her family, with whom she has always communicated via books. In Fun Home, she writes that her parents are most real to her in fictional terms, and compares her father's personal myth-making to Jay Gatsby, her mother - a "vigorous American idealist" - to a Henry James heroine.
Her parents weren't emotionally expressive, but they were artistic. "They took great pleasure in books," she says, "and all of our feelings got expressed through these artistic forms."
The memoirs are an attempt to keep that conversation going. "That's how I learned about connecting as a child, and that's how I continue to do it."
The problem, of course, is that this conversation is one-sided, with the balance of power skewed in the writer's favour. In Are You My Mother?, Bechdel circles around her mother, tracing all her unhappiness back to this relationship, implying some major unkindness, but ultimately revealing that her mother is simply more emotionally distant than she'd like.
Bechdel explores their relationship through the fiction of Virginia Woolf and the psychological theories of Donald Winnicott and Alice Miller, but is also highly personal, tracking their problems as far as the breastfeeding process. To have your parenting choices divulged, considered, often found wanting, seems painful at best. It's a problem Bechdel is aware of.
"It's a very dicey ethical line, you know? How much of her story is also my story, how much can I really tell without violating her? Those are the things I'm always asking myself, and I feel like I have hurt my mother. I have betrayed my mother. But it's something I feel I have to do, and to her credit she seems to be OK with it.
"I mean, I know she's not happy, but she hasn't cut me off."
The difficulty of having a daughter so driven to self-exposure seems especially tough when you consider the secrets her mother has been burdened with over the years. Bechdel's father, Bruce, was a troubled man, who worked part-time as an undertaker, and first appears in Fun Home pouring all his energies into renovating their house, a gothic revival mansion in small-town Pennsylvania. "Sometimes, when things were going well," Bechdel writes, "I think my father actually enjoyed having a family, or at least the air of authenticity we lent to his exhibit." What lay beneath was the affairs he was having with other men, and boys in their late teens, including the family babysitter, Roy.
Bechdel's mother must have been aware of these affairs for at least part of their marriage. It's not surprising, then, that she was emotionally withdrawn, doing her best to hold the family together in difficult circumstances.
In her second memoir, Bechdel writes that her mother abruptly stopped kissing her goodnight when she was seven, telling her she was too old. "I felt almost as if she'd slapped me," she writes. "But I was stoic. I betrayed no reaction." It was when she was 10 that she felt closest to her mother and, again, a book was key. Bechdel had been writing a diary, but over time had become obsessive about the need to be entirely truthful, a process she has written about in her memoirs. The words "I think" crept into each line (how could she possibly know anything for sure?), and eventually word upon word was scored out by a symbol signifying uncertainty.
For a short period, her mother took over, sitting with her and taking down what she had done each day. "That was a very pivotal moment," says Bechdel. "It was the first time I remembered really getting that much focused attention from her ... All the things that a normal family would express through affection or physical closeness got funnelled, for me and my mother, through that transaction of writing. That became very powerful for me."
She bonded with her father as a student in one of his English classes, and it was her love of books that led to the discovery of her sexuality. She encountered the word lesbian in the dictionary when she was 13, then found a book on the subject in the library at 19. After writing to her parents to tell them, she received a fairly warm response from her father, a more disapproving one from her mother. This was followed by a phone call in which her mother filled her in on her father's affairs. The marriage began to break down rapidly, and there were plans for a divorce.
Four months after she came out, her father was hit by a truck. Bechdel strongly believes he killed himself and wanted to write about it for years, but felt constrained. After that college essay, she wrote another piece about her family, a "memoir fragment", and sent it to her mother. It was sent back covered in incisive notes, scrawled in red ink, about her use of language. She didn't write about her family again for 17 years. When she first told her mother she was writing Fun Home, the response, was "'I can't help you, you're on your own'. [My mother] said she was not going to give me any more information about my father. I was officially cut off from that, and she's pretty much stuck to it. I can't really ask her stuff about the family any more, but sometimes she'll voluntarily tell me things".
On one occasion, her mother gave her a "wonderful trove of letters that my father had written her, so it's not clear cut. She'll divulge things when and how she wants to". Has the process of writing these memoirs deepened her family relationships or undermined them? Bechdel says it's brought her closer to her mother. "It sounds terrible, but I feel like I pay more attention to her because I know I'm writing about her. So I listen more carefully."
Having always felt constrained by her mother's critical voice, the book has helped exorcise this too. "I feel somehow that I'm able to just speak more easily, to allow myself to have thoughts and ideas without censoring them or editing them".
Still, if the books are an attempt to have a conversation with her family, the discussion seems a bit stunted. The sum total of her mother's response to this book has been three words: "Well, it coheres."
Bechdel has made an aggressive attempt to force her into a conversation and she has made a defensive decision to stay silent. "Absolutely my writing about her is an aggressive act," says Bechdel, "but in that military sense, I feel that we have a sort of truce. Like if she's OK with me writing, I'm OK with her not responding."
I can't help laughing when she says she's planning to write about her two brothers next. No stone of this family's life will remain unturned. The trouble is, she hasn't heard from her siblings about this latest book and suspects, "They're a little tired of me and my memoirs ... What I really want to write about is the whole family as a system, and how families work. That would be a way of engaging with them, in a way that I'm not able to do really in my every day life." But will they keep returning her calls?
Are You My Mother, by Alison Bechdel, is published by Jonathan Cape, £12.99. To order a copy for £10.39, including free UK p&p, go to theguardian.com/bookshop or call 0330 333 6846
• This article was corrected on Saturday 19 May to amend online subbing errors
