Italian roasted tomato and capsicum soup

Ingredients

• 2 tablespoon olive oil
• 1 onion or leek, chopped
• 1 clove garlic, finely chopped
• 500 gram tomatoes, quartered, roasted
• 500 gram red capsicum, halved, seeded, roasted
• 1 litre (4 cups) vegetable stock
• 2 cup (500ml) water
• 300 gram can butter beans, rinsed, drained
• basil leaves, to serve