Step 1

Heat the oven to 220C (200C fan)/425F/gas 7.

Step 2

Peel the sweet potatoes, then cut them into 1½cm-thick rounds and put in a large roasting tray. Season generously, then pour over the vegetable oil and toss to coat.

Step 3

Spread out the sweet potatoes in a single layer (you might need a second tray to accommodate them all), then roast for 20 minutes, until the potatoes are golden, starting to brown at the edges and cooked through.

Step 4

Scatter over the peanuts and a teaspoon of the sugar, then return to the oven for five minutes more, to caramelise. Remove and leave to cool slightly for 10 minutes.

Step 5

While the sweet potatoes are roasting, make the dressing. In a bowl, whisk the coconut milk, fish sauce, lime juice and remaining half-teaspoon of sugar.

Step 6

Finely grate in the garlic and whisk again.

Step 7

When the sweet potato has cooled a little, tip it into a bowl, add the chopped herbs, spring onions and chilli, and toss.

Step 8

To serve, drizzle over the dressing and toss again.