Sweet potato & cumin soup

Ingredients

• 1 tbsp olive oil
• 1 small onion
• 900g sweet potatoes, peeled and cut into cubes
• 450g carrots, cut into cubes
• thumb sized piece fresh root ginger, peeled and grated
• 1 tsp ground cumin
• 1.4 litres vegetable stock
• 1 tbsp of mild curry powder
• salt and pepper
• Greek yoghurt & chopped chives to garnish (optional)
• Fresh wholemeal bread to serve (optional)