Heat the oven to 220C/200C fan/gas 8. Add the oil to a large flameproof baking tray and put in the oven for the oil to heat up.

Bring a large pan of salted water to the boil, tip in the potatoes and the peelings (to impart extra flavour) and simmer for 8-10 mins. Drain the potatoes and discard the peelings. Leave to steam-dry for 15 mins, then return the potatoes to the pan, put the lid on and gently shake to lightly rough up the edges.

Remove the tray from the oven and put directly on your hob over a medium heat. Add the butter to the hot oil and, using tongs, add the potatoes to the tray, one by one, carefully turning them in the fat, and leaving a little space between them. Reduce the oven to 200C/180C fan/gas 6. Nestle the lemon thyme in amongst the potatoes, along with the garlic. Sprinkle over the sea salt and return to the oven to roast for 1 hr, turning every once in a while, until golden and crisp.