Heat the oil in a large saucepan. Add the garlic, chilli, ginger, lemongrass, coriander stalks and curry paste and cook for 2 - 3 minutes until the aromas are released.
Add the chicken stock, coconut cream and sweet potatoes and cook for 15 minutes or until the potatoes are soft. Remove the lemongrass and discard. Carefully transfer to a blender and blitz until smooth. If freezing, for best results freeze at this point, otherwise as an easier option freeze complete recipe.
Return to the saucepan, add the chicken and cook gently for 5 - 10 minutes or until the chicken is cooked through. Stir through the lime juice, sugar and fish sauce, scatter with the coriander leaves and serve.