THREE years ago, Jamie Oliver turned 40, and he really "didn't enjoy it much".

The prospect of entering his fifth decade made The Naked Chef more than a little "reflective", he admits. Meanwhile, his long-time mentor Gennaro Contaldo - who guided Oliver through his early days at the late Antonio Carluccio's Neal Street Restaurant during the Nineties - was edging towards the big seven-oh.

"He was in a similar but different reflective kind of moment," remembers Oliver. Getting away, escaping for a bit became increasingly appealing to them both. "Me and Gennaro felt we needed that time personally."

Italy, Contaldo's homeland, became the destination, and the pair spent months travelling from the northern mountains to the southern islands, across the seasons. The result is Oliver's latest cookbook and accompanying Channel 4 series, Jamie Cooks Italy.

It's not just about the duo barrelling around Italy gorging on pasta in an effort to scrub out the years though. Instead, the pair set out to learn from the last generation of Italian 'nonnas', women in their 80s and 90s who "didn't grow up with fridges, freezers, microwaves, gas, electricity - we're talking about old school," notes the Essex-born restaurateur, reverently.

The aim was to capture "a snapshot, a moment, a bit of history", and by meeting the "matriarchs of the best cooking on the planet", help preserve a way of cooking and eating that could cease with a generation.

"I am, and I think they are," says Oliver, when asked if he's worried the food of the nonnas is being gradually eroded. "Things fade, things go, things that are loved and important and really good for family nutrition, or communities or farming or fun, they can be going for hundreds and hundreds and hundreds of years, [but] it only takes five years for something to completely die off."

"Every single nonna, without question, was like, 'Share this, get this to as many people as possible, people aren't cooking that in this village anymore'," he continues. "It's fair to say that the new generation of young Italian boys and girls are not cooking like the one before, and the one before and the one before that."

Strangely, he says the recipes in the book are "almost smoke and mirrors" - the food is important, but with every encounter, whether it was making orecchiette by hand with nonna Graziella in Puglia, or eating sweet and sour rabbit with nonna Marina in Salina, it increasingly became apparent that Oliver and his crew were working on more than a cookbook, they were making a record of "life and being grateful".

"It's about love and seizing the moment," he says, shaking his head, keen to not sound overly romantic. "We laughed a lot, and we cried quite a lot.

"There were some really f****** intense moments."

He tells of making tiella, with nonna Linda in Puglia, a baked long grain rice dish bejewelled with tomatoes, courgettes and mussels ("She shucked these mussels, not for mussels' sake, but almost as a seasoning - my god it was delicious").

"She was so welcoming," remembers Oliver. "I was introducing everyone outside in this square, but I kept doing really s*** Italian, so she didn't understand what I was saying. I kept getting it wrong, and every time I got it right, the bells would ring.

"We started giggling - she hadn't got a clue who I was - then we just giggled like children for 15 minutes."

Eventually they got to around to the tiella, and "while it's cooking you've got an hour to talk. We're talking about how hard the winters were and life and money and family, and the loss of her husband.

"Then it was like, 'How many kids have you got? [Oliver has five children with wife of 18 years, Jools], and then she pulls out this jar with a baby [in it]. It was one that was lost. It takes your breath away," says Oliver, visibly moved. "But that's completely normal [for certain generations in Italy], and just like cooking and technology, and opportunities and mortality, and the concept of a crematorium, that's very, very new.

"It's real, so then the conversation becomes about loss and love," he continues, "but also about the dish. As a parent, food's originally used to nourish your growing baby, and then your child, and then your teenager, and then they leave and you use food to bring them back because you want to see them again. You use it like a magnet, it's like currency, but the meaning of the currency is different - it's quite a fascinating thing."

For Oliver, who worked in the kitchens at the famed River Cafe, Italians ("They're just crazy enough") and Italian food have always held a certain charm.

He blames its winning combination of "high flavour, simplicity and comfort - a lot of it makes you feel good", and it not being "too elegant or over crafted". Instead of demanding intricately diced vegetables and that you own a sous vide, "there's none of that, it's like, go and find this incredible stuff, get some of that, rip that up, tear that up, bash that, get that in there, drizzle", jabbers Oliver, hands flying. "It's quite an accessible, simple, delicious cuisine."

And no, the nonnas weren't too zealous with him when sharing their recipes. "They'll go, 'You can do that if you want', because they're mums, right? Yes, they're strict about the recipe, but if two more people turn up, they've got to stretch it, and if it's not in season, they've got to use something else."

Most of the nonnas he and Contaldo met were from quite poor backgrounds, "so they were cooking fabulous food with not much resource or money. That's really empowering and really, really inspiring to see," says Oliver, "particularly as - and largely only in Britain - we associate good food, loving food, with being rich. Although it's easy to think that, it couldn't be further from the truth.

"It's about knowledge," he continues. "If you truly love something, regardless of how old or what people think of you, it's still OK to hunt and search and grovel for knowledge.

"And if you say, 'Do you want to go to this Michelin-starred restaurant for dinner, or go to nonna Marina?' I'm with Marina every time."

HOW TO MAKE JAMIE OLIVER'S LASAGNE WITH SLOW-COOKED FENNEL, SWEET LEEKS AND CHEESES

You'll want to eat the whole thing on your own.

"Being really single-minded in our commitment to drag out all the sweet deliciousness from fennel and leeks, this lasagne is an absolute cracker," promises Jamie Oliver.

"Made and layered up with love, it's a confident and classy centrepiece."

Give it a go...

Ingredients:

(Serves 8-10)

4 large leeks

3 bulbs of fennel

6 cloves of garlic

50g unsalted butter

1/2 a bunch of fresh thyme (15g)

125ml Soave white wine

75g plain flour

1.5L whole milk

1 whole nutmeg, for grating

50g pecorino or Parmesan cheese

100g Taleggio cheese

400g dried lasagne sheets

125g ball of mozzarella cheese

100g Gorgonzola cheese

Olive oil

Sea salt and black pepper

Method:

1. Trim and slice the leeks and fennel, then peel and finely chop the garlic. Melt the butter in a large pan over a medium heat, strip in most of the thyme leaves, then stir in the veg. Season, then fry for 15 minutes, stirring regularly.

2. Pour in the wine, cover, and cook for 30 minutes, or until soft and sweet, stirring regularly and adding splashes of water, if needed.

3. Stir in the flour for a few minutes, then gradually add the milk, a splash at a time, stirring constantly. Simmer until thickened, stirring occasionally. Finely grate in half the nutmeg. Remove from the heat, finely grate in half the pecorino, tear in half the Taleggio, and stir well. Taste and season to perfection with sea salt and black pepper, if needed, and leave to cool.

4. Preheat the oven to 180oC. To assemble, layer up the sauce and pasta sheets in a large baking dish, adding little bombs of mozzarella, Gorgonzola and the remaining Taleggio as you go, finishing with a final layer of sauce. Finely grate over the remaining pecorino and any other bits of cheese, then bake for 40 minutes, or until golden and bubbling.

5. Pick the remaining thyme leaves, toss in a little oil, and scatter over for the last five minutes. Leave to stand for 15 minutes, then dig in.

HOW TO MAKE JAMIE OLIVER'S LIMONCELLO TIRAMISU WITH MASCARPONE, CHERRIES AND WHITE CHOCOLATE

A light and super summery dessert.

"Of course, this is not a traditional tiramisu, but the layering of the sponge and silky vanilla mascarpone provides the link to the dessert we all know and love," explains celebrity chef, Jamie Oliver.

"Using cherries, limoncello and white chocolate gives you a lighter-feeling dessert that is hugely enjoyable, inspired by long summer days along the Amalfi coast."

Ingredients:

(Serves 8)

2 oranges

200ml limoncello

4tbsp runny honey

200g sponge fingers

200ml good espresso (cold)

250g mascarpone cheese

250g natural yoghurt

1tsp vanilla bean paste

250g ripe cherries

Extra virgin olive oil

100g white chocolate (cold)

Method:

1. Use a speed-peeler to peel strips of zest from the oranges into a small pan. Squeeze over all the juice, add 100ml of the limoncello and two tablespoons of honey, and simmer over a medium heat until you have a thick syrup.

2. Cover the base of a 24cm serving bowl with half the sponge fingers. Mix the cold espresso with the remaining limoncello, then drizzle half of it over the sponge layer, pressing down lightly to help it absorb the coffee mixture.

3. Whisk together the mascarpone, yoghurt, vanilla paste and remaining two tablespoons of honey until smooth, then spoon half into the bowl in an even layer. Remove the stones from the cherries, tearing the flesh over the mascarpone. Lay the remaining sponge fingers on top, drizzle over the rest of the coffee, and finish by spooning over the remaining mascarpone.

4. Spoon the syrup and candied peel over the tiramisu, and drizzle with a little extra virgin olive oil. Cover and pop into the fridge for at least four hours, or overnight.

5. Shave or grate over the white chocolate to finish.

Calories: 584kcal

Jamie Cooks Italy by Jamie Oliver, photography by David Loftus, is published by Penguin Random House (c) Jamie Oliver Enterprises Limited (2018 Jamie Cooks Italy), priced £26. Available now.