Heat the olive oil in a large saucepan over a medium heat, then add the onion and garlic and cook for 4 minutes until soft, stirring often.
Add the carrots and sweet potatoes, then cook for 3 minutes, stirring often.
Stir in the ground cumin and cook for a further minute.
Pour in the hot vegetable stock and increase the heat to high. Cook until the soup bubbles, then reduce the heat to low and cook, uncovered, for 30 minutes.
Blend the soup with a hand held emersion blender until smooth, or else carefully transfer to a blender to whiz. Season with salt and pepper.