There is one ingredient that people often overlook when cooking roast potatoes at home, which prevents them from becoming extremely crispy. Potatoes are a staple in Christmas dinners and Sunday roasts across the country, so getting this right is essential when they are cooked on special occasions.

Incorporating this one simple ingredient into roast potatoes ensures you execute perfectly crispy exterior roast potatoes according to New York Times food columnist and author of New York Times bestseller book: The Food Lab: Better Home Cooking Through Science, James Kenji Lopez.

Chef Kenji describes his recipes as the "best crispy and crunchy roast potatoes he's ever had". Chef Kenji reveals the secret lies in incorporating 1/2 teaspoon (4g) of baking soda into the boiling water and cooking your potatoes until fork tender but not breaking into pieces.

In his detailed cooking video he showed the first step of adding 2 quarts of boiling water, 1 ounce of salt and 1/2 teaspoon of baking soda, and 4 chunks of chopped potatoes and boil for 10 minutes.

Boiling potatoes in alkaline water with baking soda breaks their exteriors, creating a starchy slurry that crisps up in the oven, enhancing both texture and flavour.

Whilst the potatoes are cooking, he proceeds to prepare the garlic (3 minced) and a handful of rosemary mixture with 5 tablespoons of oil and cook on medium heat, then strain off the oil.

Chef Kenji then uses the infused oil to generously coat the potatoes. He said: "The goal here is to be a little bit rough on them so a pasty mash potato-like layer builds up on the exterior."

Finally, add a sprinkling of salt and pepper, then bake in the oven for 20 minutes at 450 degrees.

He said after 20 minutes, "give them a careful flip with a spatula or your fingers". Advising viewers on how to know when the potatoes are perfectly roasted, he said: "When they are deeply brown and crispy."

Viewers were quick to react in 'The Food Lab: How to Roast the Best Potatoes of your Life' YouTube video comments.

One said: "The baking soda trick is a secret I'll take to my grave. Grazie."

Another commented: "Made these today. Excellent. Not a single leftover morsel. A new family favourite."