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1
Set the oven to 160 °C. Do not line the rack or wrap the potatoes; direct dry heat on the oven rack is required. Place the sweet potatoes directly on the centre rack, leaving space between each one for air circulation.
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2
Roast at 160 °C for 60–75 minutes without disturbance. This is where the dish lives or dies: the low temperature must be sustained for the full duration so that the beta-amylase enzyme — active below approximately 70 °C — has the maximum time to convert the potato's starch to maltose before the interior temperature rises beyond that threshold. Rushing this stage with higher heat destroys the enzyme before sugar conversion is complete, producing a starchy, less sweet result. The potatoes are ready for the next stage when the skin has darkened and the flesh yields deeply to firm pressure with a cloth — the interior should feel molten rather than resistant.
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3
Raise the oven temperature to 220 °C. Return the potatoes for a further 10 minutes. The skin is ready when it is visibly blistered and taut, with darkened, lightly caramelised patches; a thin, crisp surface should contrast with the soft interior beneath.
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4
Remove from the oven and rest uncovered for 5 minutes. This allows the internal temperature to equilibrate throughout the flesh. The aroma at rest should be distinctly honey-like and caramelised — earthy sweetness with no raw or starchy note.
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5
Serve whole, split lengthways at the table. The interior should be toro — molten, honey-coloured, and glistening. A clean split will reveal an amber-yellow, almost lacquered flesh with no white or floury centre remaining.