Nadiya Hussain can date exactly the first time she came to this restaurant – Olive Tree, a big lively Turkish grill on a prominent corner of one of Milton Keynes’s 1970s precincts. It was seven years ago, the week her family moved to the new town from Luton, where she grew up. “We were living out of boxes and needed somewhere quick and halal,” she says. “But we’ve been coming back ever since. Our three kids love it – they were so jealous when they heard I was coming here with the Observer…”

Seven years also dates the moment when the family’s life turned upside down when Nadiya became Bake Off champion and instant national treasure. You don’t have to spend five minutes with her to see why she joined that exclusive group of TV competition veterans – my list stops at Harry Styles and Susan Boyle and her – who have sustained their 15 minutes of fame. She is a brilliant mix of things. She talks 20 to the dozen as we order her family favourites – “hummus because it comes with great bread, for sure the lamb’s liver – delicious! – the adana skewers, if you like spicy, halloumi, chops” – but she also has a kind of quiet poise.

She’s physically small, but her smile is large. Her determination is to resist stereotype. “Obviously I kind of straddle lots of different worlds,” she says, early on, answering a question about fame. “You know, I’m a woman, a mother, I’m Bangladeshi. I’m Muslim. I’m British. I think there’s an expectation from every community that I fly their flag. In some ways that means I can’t win. I can make a Cornish pasty and some people will say: that’s not authentic. And the same if I do a Bangladesh dish. So I just try to do what I like.”

One of the fascinations of her 2020 memoir, Finding My Voice, is that Bake Off barely gets a mention. The struggles of her life, with horrible bullying at school, with invasive memories of an episode of sexual abuse from a distant family member as a child, with the strictures of parents keener to tell her what she could not do (go to university, become a midwife) than what she could, are the challenges that she dwells on. It’s still a long road for her to overcome what she calls “panic disorder and PTSD” from those experiences. Before she ever met Mary Berry she had got herself on to an Open University course while working and with three children under seven. The cupcakes and what has happened since – books, TV series, a newspaper column in the Times, an MBE – are just ongoing public proof for her of more private victories.

“I grew up around a generation of women who were thrifty and worked hard and could multitask,” she says of her mother’s circle, “but I didn’t grow up among happy women. I need my daughter to know she can do all of those things but be happy as well. I grew up being told: ‘You can’t do that, it’s not ladylike.’ That’s been the quiet whispering of my entire life. I used to think: fight it, fight it, fight it. That fight isn’t over for my daughter. I always tell her: in case plan A doesn’t turn out, always make sure you have running away money.”

As we share out the liver and the halloumi she talks me through her day so far. “I always get my work emails out of the way first. It’s been a busy time because I have this new book out and I’m finishing my TV series. But I’ve done emails by 10am, and then as always I prepared for dinner tonight. I’ve done a chicken curry with brussels sprouts using the whole chicken. The neck and the knuckles. My sister and her family are coming over later so we’ll eat together. Though maybe not much for me after this lunch.”

I was struck in her memoir by how she was formed by sibling relationships – she has three sisters and two brothers. Are they still all close?

“I could have written about every family member,” she says. “My mum and dad raised me, but they were not the ones who listened to me when I cried. My siblings have always been the backbone.”

There seems quite a strong hierarchy among them – Nadiya is the third oldest. How have her older sisters reacted to her celebrity?

“My big sister finds it really funny,” she says. “Even to this day, when I go to her house – though she has a dishwasher – she leaves her washing up for me: ‘You’re not too famous to do my dishes.’”

She goes along with that?

“Of course,” she says. “When my sisters come over and stay at my house, I will give them my bed and sleep on the floor. Those things are important to me. When I go to my parents’ house, the first thing I do is get the vacuum cleaner out.”

She had an arranged marriage when she was 20. Though she had known of her future husband’s existence for six months, they got engaged the day they met and were married 10 days later. Does she watch that programme Married at First Sight?

“All the time. It’s very addictive. People ask me, will you find a husband or wife for your own kids? Absolutely no way! We got very lucky. But I didn’t want to bring my children up in a family like the ones I grew up around, which were often built around duty rather than love.”

Though she says she and her husband “are very different characters”, they share core beliefs. “Faith is the bookends of our family life. When the sun sets, you know, we close all the blinds, put on the lamps and we all sit and we pray together every day.”

The other binding force is obviously mealtimes. What does she like to cook at the moment?

“My kids love offal. I cooked tripe yesterday – I do it in the garage because it’s a bit smelly. We’ve been doing lots of broth using chicken feet. When they were younger they liked stuff like fish pie, lasagne. As they have become older, they are far more interested in Bangladeshi cooking. But: offal and endless banana bread. It’s a mixture of those two at the moment.”

On cue, one of several such interruptions to our lunch, a man from a neighbouring table comes up to praise Nadiya for the chocolate cake she made on the previous night’s TV programme. “You cut a very small piece out and I thought: can I have the rest of it?”

“I love it when older English men come up like that,” she says, when he has left. “When my grandma came to this country, she was scared of English people. It would still shock her to see a man like that talk to me so easily. She’ll still tell me: just be grateful and keep your head down.”

This despite the fact that her granddaughter baked the Queen’s 90th birthday cake. “I’d met the Queen before,” she says. “The first time, she said to Prince Philip: ‘You know, this is the young lady who won the baking competition.’ I was like: life made, right? I always wonder what my grandad would have thought if he had been alive. He worked so hard to be accepted in this country, was nearly killed twice after being beaten up by racist thugs. If I’d got my MBE while he was alive, would he finally feel like we were accepted?”

We talk a bit about her extended family in Bangladesh who are rice farmers and buffalo farmers. She visits every few years. Some of that culture is in her blood, she says. “Bangladeshis waste nothing. When you killed an animal, you sold the skin for leather. And then you would carve out the skull for an ornament. And then you would cook every part of it. I’m very like that.”

It sounds, among other things, I say, like good preparation for I’m a Celebrity… She must have been asked?

She laughs. “I’ve been asked on them all. I couldn’t do Strictly because I think it would kill my husband to watch. But I do love the idea of the jungle. I’m good with creepy crawlies. I love snakes – I just bought my son a blue-tongued skink – though I’ve been bitten by them in Bangladesh on about 12 occasions.” She pauses, smiles. “Of course, I don’t think I’d win or anything …” On the evidence of one lunch, I certainly wouldn’t bet against her.

Nadiya’s Everyday Baking (Michael Joseph, £25) is out now. To support the Guardian and Observer order your copy from guardianbookshop.com