Thai prawn curry soup

For the paste:

• 2 spring onions, trimmed and roughly chopped
• 1 lemongrass stalk, trimmed and roughly chopped
• 1–2 green chillies (to taste), deseeded and roughly chopped
• 2 cloves garlic, peeled and roughly diced
• 2.5cm root ginger, peeled and roughly chopped
• 2 dried kaffir lime leaves
• Large handful fresh coriander, roughly chopped
• 2 tablespoons reduced-salt soy sauce
• 1 teaspoon fish sauce

For the soup:

• 400ml can light coconut milk
• 250ml reduced-salt stock
• 1 red pepper, deseeded and chopped or finely sliced
• 175g baby sweetcorn
• 200g pak choi, roughly chopped
• 200g sugar snap peas
• 200g raw or pre-cooked king prawns
• Lime wedges, to serve