Pea, mint & spring onion soup with Parmesan biscuits

INGREDIENTS

• 1 tbsp olive oil
• knob of butter
• ½ bunch spring onion , sliced, plus a few extra to serve
• 1 potato , cut into small dice
• 1l hot vegetable stock
• 900g frozen petits pois
• ½ small bunch mint , leaves picked, plus a few extra to serve
• 85g Parmesan (or vegetarian alternative), very finely grated