Pea & mint soup

INGREDIENTS

• 1 bunch spring onions , trimmed and roughly chopped
• 1 medium potato , peeled and diced
• 1 garlic clove , crushed
• 850ml vegetable or chicken stock
• 900g young peas in the pod (to give about 250g/9oz shelled peas)
• 4 tbsp chopped fresh mint
• large pinch caster sugar
• 1 tbsp fresh lemon or lime juice
• 150ml buttermilk or soured cream