Heat oil in a large saucepan and cook the onion and garlic over a medium heat for 5 minutes, stirring occasionally, until beginning to brown.
Add the sweet potato, stock, tomato paste, bay leaf, paprika and cayenne and salt according to taste. Bring to the boil, reduce heat and simmer, covered for 45 mnutes.
Take the pan off the heat and remove the bay leaf. Blend the soup to a smooth consistency with a stick blender. Add 1/2 cup (125ml) of the cream and saffron infusion and stir well.
Taste the soup to check the seasoning, adding more pepper or salt if necessary.
Return to the stove and gently reheat for a minute or two, stirring constantly. Ladle into soup bowls and serve topped with a swirl of cream and fresh coriander leaves.