Thai chicken and sweet potato soup

INGREDIENTS

• 1 tsp olive or rapeseed oil
• 2 garlic cloves , chopped
• 1 red chilli , deseeded and chopped
• 2cm chunk root ginger , chopped
• 1 stalk lemongrass , bashed
• 1 x 25g pack coriander , leaves and stalks chopped separately
• 2 tbsp red Thai curry paste
• 750ml chicken stock (made with 2 stock cubes)
• 1 small can (160ml) coconut cream
• 500g sweet potatoes , peeled and roughly chopped
• 2 skinless chicken breasts , sliced
• 1 lime , juice only
• 1 tsp sugar
• ½ tsp fish sauce
• crusty bread , to serve (optional)