Whether it's your mum who makes the best, or the roast shop down the road, this Christmas, you can up your roast potato game thanks to the inside word from a Michelin star chef.

Some might argue the success of a Kiwi Christmas feast all comes down to that dish of roast taters: they should be extra crispy on the outside and dense but fluffy on the inside. How you cook them can be the maker of a memorable festive feast and anything short of crispy perfection may never be entirely forgiven (so, no pressure).

Enter Ashley Palmer-Watts, the chef director at London's two-Michelin-star restaurant "Dinner" by Heston Blumenthal - and a roast potato connoisseur.

He prioritises roast potatoes above most things, telling the Telegraph: "I am the most pedantic person about roast potatoes. I could talk all day about them."

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Palmer-Watts says perfect roast potatoes should have "a perfectly cooked inside and an almost glassy-crisp outside." The key components to achieving this? Patience and time.

But none of this is possible if the potatoes themselves are wrong. The best potatoes change with the seasons as the level of sugar fluctuates in each variety during storage. Dry matter – the non-water part of the potato – also varies. Too much and the potatoes will fall apart when cooked, too little and they'll be soggy. The perfect mix of both is crucial.

Simmer down

Palmer-Watts warns cooking them in fast boiling water "is one of the key mistakes". It crumbles the edges and leaves the centre underdone. Instead, simmer them gently until they are cooked through.

"You want to remove as much water as possible, and cooking the potatoes dries them," he explained to the Telegraph. A dry inside is essential, the crust won't crisp up properly otherwise.

A key mistake is cooking potatoes in fast boiling water which crumbles the edges and leaves the centre underdone. Photo / Getty Images
A key mistake is cooking potatoes in fast boiling water which crumbles the edges and leaves the centre underdone. Photo / Getty Images

Confusing yes, cooking potatoes in water makes them drier: "Water will always migrate to a greater mass of water," expains Palmer-Watts.

This goes with the reasoning that it's also better to boil the potatoes rather than steam them. The water needs to be salted, too – and not just for flavour. "It gives a crisp glassiness to the outside of the roast potato."

Another no-no is shaking your potatoes in a colander after draining them. They should be falling apart a bit already, but they need to cooled, which will dry them even more.

Once the inside is perfected, it's time to get that golden exterior.

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An unlikely oil

Yee of solid frying nouse may be surprised to learn Palmer-Watts' secret is a mild extra-virgin olive oil. "You shouldn't use a very high heat," he explained. That's especially important if you use duck or goose fat, which develops off flavours if the oven is too hot.

He highlights the importance of knowing your own oven, adjusting timings and temperatures to achieve perfection and giving your tray a turn during cooking.

While the smell will waft through your home and excite your taste buds, so should the sound. "You can hear them," Palmer-Watts claims. A distinct crackling, sizzling noise from the roasting tin means "those are happy potatoes".

Key tips for Ashley Palmer-Watt's perfect roast potatoes

1. Choose the highest "dry matter" potato for the time of year.
2. Cut the potatoes to create as many sides as possible.
3. Rinse potatoes thoroughly in cold water to remove the starch before cooking.
4.  Use 5g salt for every litre of water.
5. Cook the potatoes without boiling them hard, They're done when a thin-bladed knife can be easily pushed into the centre.
6. Baste them with the oil in the tin (adding more if you need to).

Palmer-Watts also likes to add unpeeled garlic cloves and sprigs of rosemary during the cooking process.

See more delicious roast potatoes recipes on Bite
Roast potatoes