Prepare the potatoes: Scrub the potatoes clean, but leave the skins on — they become wonderfully crispy. Cut them into even 3cm chunks. Place them in a large bowl and cover with cold water. Swish them around with your hand until the water turns cloudy. Drain and repeat once more. This removes excess starch, which is the enemy of crispiness.

Parboil the potatoes: Transfer the rinsed potatoes to a large saucepan and cover with fresh cold water. Add a generous teaspoon of salt. Bring to a boil over high heat — you'll see the water bubbling vigorously and the potatoes beginning to dance. Reduce the heat to a simmer and cook for 8 minutes. The potatoes should feel just tender when pierced with a knife but not falling apart; the edges will look slightly softened and the skins will have a faintly translucent appearance.

Create the roughed-up surface: Drain the potatoes in a colander. Let them steam dry for 2 minutes — you'll see wisps of steam rising. Return them to the dry saucepan, add the cornflour, and put the lid on. Shake the pan vigorously for 30 seconds. When you lift the lid, the potatoes should look slightly battered and fluffy on the outside, with a fine coating of cornflour. This rough surface is what creates that incredible crunch.

Heat the fat: Place a large, heavy-based frying pan (non-stick is fine, but cast iron is best) over medium-high heat. Add the vegetable oil and butter. Watch as the butter melts and begins to foam — you should hear a gentle sizzle. When the foaming subsides and the butter smells nutty and turns a light golden colour, the fat is ready.

First sear: Carefully add the potatoes in a single layer. Do not crowd the pan — if necessary, cook in two batches. Listen for a loud, steady sizzle as the potatoes hit the hot fat. Leave them undisturbed for 4 minutes. Peek underneath: the bottoms should be a deep golden brown with jagged, crispy edges.

Flip and finish: Turn each potato chunk with tongs or a spatula. Add the smashed garlic cloves, rosemary, and thyme sprigs. Cook for another 6-8 minutes, turning every 2 minutes, until all sides are deeply golden and the potatoes feel light and hollow when you nudge them. The kitchen should smell of roasted herbs and caramelised potato. The crust will look craggy and textured, with darker spots where the cornflour has caramelised.

Rest and season: Transfer the potatoes to a plate lined with kitchen paper. Let them rest for exactly 2 minutes — you'll hear a faint crackling sound as excess oil is absorbed. Discard the garlic and herb sprigs. Sprinkle immediately with flaky sea salt, black pepper, smoked paprika if using, and the chopped parsley. Toss gently to coat.

Plate for impact: Arrange the potatoes on a warmed serving platter or a wooden board in a single, slightly overlapping layer. Tuck lemon wedges around the edges. Finish with one final pinch of flaky salt, letting the crystals catch the light. Serve immediately while the crust is still shatteringly crisp.