It is after 8pm on Valentine’s Day and a queue is still stretching around the block. Inside the kitchen store in a suburban Los Angeles shopping mall, Nigella Lawson radiates charm and nervous energy, despite starting her day at 5am with a hangover and having been stuck in LA’s notorious rush-hour traffic for three hours.

Her famous curves are poured into a shocking pink ‘Diva’ wiggle dress as she pouts and poses for pictures and swaps recipes with overweight American housewives, remaining unfailingly cheerful.

Much later, as the last satisfied customer leaves the shop clutching a signed copy of the domestic goddess’s new book, she turns to me and says: ‘I was in a terrible state earlier in the car, a total nervous wreck. I loathe being late. It is the epitome of bad manners. I’d hate anyone to think I was rude.’

It seems extraordinary that a woman who has built an empire estimated to be worth £10?million with her unique, lusty approach to food, still cares so much about what people think.

Yet in our wide-ranging and candid interview, Nigella is typically forthright about that infamous picture of her in a burkini, how she protects her children against the perils of fame, how cooking keeps her sane and why those ‘wiggle’ dresses give her the confidence to face the cameras.

‘Like any woman, I dress for comfort and I find those dresses the most comfortable,’ she says,

‘Everything in my life comes down to basic laziness. I buy the dresses, mostly online, and I’ve learned what flatters my figure and what feels good and is affordable. It’s as simple as that. It’s funny when people pay so much attention to my appearance because, quite honestly, it’s the thing I think least about. I rarely look in a mirror.

‘The wiggle dresses are a uniform. They help me feel confident when I’m working. In private, I’m happiest in a dressing gown and FitFlops.’

We meet earlier at a Hollywood hotel to discuss Nigella’s current quest to conquer America. Her new TV cookery show – The Taste – has earned her millions of new fans here and she’s on a gruelling ten-day book tour.

Curling her legs underneath her on the sofa, Nigella seems blissfully unaware of the mesmerising effect she is having on every man in the room. The waiter hovers hopefully and practically purrs with delight when she bats her long eyelashes and orders water with a spritz of cranberry.

She laughs when I tell her I’d expected her to be ‘more posh’, and says: ‘Yes, I don’t understand why people think I speak with a mouthful of plums. I sound pretty normal, don’t I?’

At 53, her skin is alabaster white; flawless and poreless. She wears no jewellery except a simple wedding band from her husband, art collector Charles Saatchi, and a tiny gold charm necklace also from him. I ask what he bought her for Valentine’s Day.

‘I’m the Grinch of Valentine’s Day,’ she says, ‘I think it should be about teenagers and those who are single. I think if I said I wanted to do something for Valentine’s Day or made a big fuss Charles would think I’d gone slightly mad.’

Although it is 80F, outside she shuns the sunshine, preferring to remain indoors. I remind her of that burkini shot when she was photographed on an Australian beach covered head-to-toe in swathes of black fabric.

She rolls her eyes. ‘I still have the burkini and will always wear it because I don’t like the sun on my body. I’d worn it for years and no one ever noticed it was me but then I was shopped by an Australian journalist and those pictures came out.’

She is looking particularly trim. What does she think of the obsession about her fluctuating weight?

‘I’ve actually not lost that much at all,’ she says grabbing a handful of soft tummy flesh. ‘That burkini picture made me look a lot fatter than I was because it was wet and stuck to every curve, lump and wobble. I’m not thin. I go up and down in my weight.

‘And I don’t worry about ageing because it’s one of the most pointless things to worry about. I know this sounds sanctimonious but when the alternative is, actually, being dead, why worry?’

Nigella’s first husband, the journalist John Diamond, died of throat cancer when he was 47. She had two children with him, Cosima (known as Mimi), now 19, and Bruno, 16.

Her mother Vanessa Salmon (heiress to the Lyons catering fortune, who split from her father, former Chancellor of the Exchequer Nigel Lawson when Nigella was a teenager) died of liver cancer at 48. Her younger sister Thomasina died from breast cancer at 32.

It is, she says, the spectre of those premature deaths that has shaped her philosophy on life. ‘I equate thinness with sickness. It’s so awful when you see people really emaciated, when thinness is a torture.

‘I saw both John and my sister get incredibly thin and fade away in a cruel way. It would be really weird to me to want to emulate that look.

‘I’ve been through such a lot that it makes me more of a risk-taker at work. Failure at work doesn’t worry me. It’s not life-or-death.

‘I don’t know how healthy I am  (she touches the wood of the sofa). I do Pilates, I walk.’ She adds: ‘I eat proper food. I don’t graze. I like meals. When I graze I feel permanently unwell.

‘If I’m watching a film with the children and they’re eating crisps I will eat one with them. But I still cook every night. It’s important for a family to eat together. Now I have teenagers it’s impossible to get them up in time for Sunday lunch but we always eat together on Sunday evenings.’

I ask whether Charles, who famously lost three stone on a diet of nine eggs a day, is still thin. ‘He’s not on the egg diet any more and he’s perfect,’ she replies with a wink.

What about his smoking habit? Isn’t it hard to be with a man who continues to smoke when you’ve suffered the loss of a husband to a smoking-related cancer? For the first time her smile freezes. She fiddles with her hair and says: ‘I don’t smoke but I enjoy passive smoking. Charles does enjoy it a lot. He’s a grown man. I can’t tell him what to do.’

The couple live in a £12.3?million home in Chelsea filled with pieces from his vast contemporary art collection including works by Tracey Emin, Damien Hirst and Jeff Koons.

Nigella says she mostly in a dressing gown and slippers when at homeNigella says she mostly in a dressing gown and slippers when at home

As for her defining label, no one knows who came up with ‘domestic goddess’. ‘That was said in irony,’ says Nigella. ‘I’m no goddess and that was the whole point. I do take exception when I’m called “self-styled domestic goddess”. It was a joke!’

As if to underline her point she adds: ‘I’m unglamorous. I read in bed on my iPad so I don’t have to turn the light on and disturb my husband. I read somewhere that the blue backlight interferes with your melatonin and sleep pattern so I wear special orange glasses like the ones snipers wear.

‘I cook in my dressing gown. I wear gentlemen’s gowns from Turnbull & Asser. I like their orange striped ones in cotton – they have pockets which are very useful to put everything in.’

She goes on: ‘I’ve got a bad Ocado habit (referring to the grocery delivery firm) but I also shop the old-fashioned way. One of the people I follow avidly on Twitter is my local fishmonger. I see what his catch is then I direct-message him with my order and waddle over and get it.’

When I ask about the horsemeat scandal, she turns serious. ‘It’s extraordinary. They police these labels so ferociously. When I bake a cake for the school fete I have to put a list of all the ingredients on because some kids have nut allergies.’

She adds: ‘People need to change their attitude towards meat. We’ve become used to the notion that expensive meat like beef should be eaten regularly and should be cheap. But it can’t be. We should eat less but better quality. It’s easy for me to say that because I’m lucky and can afford it. But good meat will always be expensive.’

She has eaten horsemeat – her parents, both Francophiles, would order it in restaurants during family holidays to France because it was cheaper than beef. ‘It tastes like a sweet version of beef.’

She says claims that some horsemeat had been contaminated with cancer-causing chemicals is ‘frightening’ and understands why that could easily turn a person paranoid.

She says: ‘I protect myself by cooking my own food as much as possible. When I go to a restaurant I try not to focus on what’s going on in the kitchen. I worked as a waitress. I’ve seen what goes on back there.

‘Being in your own kitchen feels safe, you know exactly what’s in the dish. It’s yours and made with love.’

Nigella with her late husband John Diamond: Like John, she says her husband Charles Saatchi also enjoys smokingNigella with her late husband John Diamond: Like John, she says her husband Charles Saatchi also enjoys smoking

It was going to boarding school that led to her love of home cooking. ‘As a child I wasn’t into food at all. I didn’t eat. Being sent to school at 11 made me appreciate the good food we had at home. My mother was a good cook. My favourite recipe is still her Praised Chicken. It’s chicken and vegetables in a big pot. I feed it to my children. They never met my mum but it brings me comfort that they are eating her food.’

She admits her cooking is not ‘challenging’ – she sees it as ‘therapy’.

‘I really got into cooking at Oxford. I’d go to the covered market and get a big bag of onions and make a massive vat of onion soup. I learned to cook because I had to make cheap food taste good.’

Could she, I wonder, imagine a world without food – or the odd glass of wine? She grimaces and admits having a hangover after drinking too much wine the night before with fellow TV chef Ludo Lefebvre.

‘I’m not a cook who always has a bottle on the go. I’ll drink with friends or when I go out but to be both an eater and drinker would mean I’d have to do more exercise than I’m prepared to do. I have to choose one and it’s food.’

She reveals that her children joke about her mothering, calling her ‘Medical Mama’ because she is always ready with a pill, potion or diagnosis. Perhaps the hands-on approach is all part of her determination to shield them from what she calls ‘the downside of fame’. And does it work? Well, she tells me, her daughter has a job and has asked Nigella to cut off her allowance.

She says: ‘I think it would ruin their lives to give them a lot of money while I’m alive. I grew up with a famous father and I know how embarrassing it can be.’

Back in the kitchen shop, Nigella prepares to leave. She is flying out to San Francisco the following morning and is already ‘obsessing’ about the pizza take-out she is thinking of ordering. ‘If I’m hungry, I go into a melt down,’ she warns.

She studies a paring knife on sale for $250 and gasps: ‘I could never spend that on a knife!’ Then she’s off, with a typical no-nonsense serving of advice: ‘Comfort food is comfort food wherever you are and it always comes down to roast chicken and mashed potatoes in the end.’

Nigellissima: Instant Italian Inspiration is out now.