Sweet potato & lentil soup

INGREDIENTS

• 2 tsp medium curry powder
• 3 tbsp olive oil
• 2 onions , grated
• 1 eating apple , peeled, cored and grated
• 3 garlic cloves , crushed
• 20g pack coriander , stalks chopped
• thumb-size piece fresh root ginger , grated
• 800g sweet potatoes
• 1.2l vegetable stock
• 100g red lentils
• 300ml milk
• juice 1 lime