Preheat the oven to 200°C, gas mark 6. Slice the kernels from the cobs and tip onto a large baking tray. Drizzle with 1 tbsp oil and mix well. Roast for 20-25 minutes, stirring halfway, until tender and light golden brown.
Set a saucepan with the remaining oil over a medium heat. Add the onion and cook for 10 minutes, until softened. Stir in the garlic and cook for 1 minute more. Add three-quarters of the corn, pour in the coconut cream and vegetable stock and season.
Gently warm through over a low heat, then transfer to a blender and blitz until completely smooth. Return to the pan and bring to the boil briefly. Reduce the heat to a simmer, stir in the lime juice and season.
In a small bowl, mix together the remaining sweetcorn, lime zest, chilli and coriander.
To serve, divide the sweetcorn soup among bowls and garnish with the chilli-lime salsa.