Preheat your oven to 200°C/Gas 6. Set a roasting dish on the top shelf to heat up.
Peel your sweet potatoes. Cut into 2-3cm cubes. Tumble into the warmed roasting dish. Gloss with 1 tbsp oil. Season. Cut 1cm off the pointy end of your garlic. Tuck it into the dish with the sweet potato.
Roast for 30 mins or till everything is mashably tender.
Crush the cardamom pods to reveal the little seeds inside. Crush the seeds in a pestle and mortar or on a chopping board with the bottom of a glass till powdered.
Put the roasted sweet potato cubes into a food processor or blender. Squeeze in the soft, tender garlic cloves from their skins. Add the ground cardamom and the coconut milk. Blend till smooth.
Taste. Add more stock or water and more cardamom or seasoning as needed. Taste and tweak till the soup is just right for you.