Sweet potato-topped cottage pie - Good Food Middle East

Ingredients

• 1 tbsp olive oil
• 1 onion, chopped
• 1 carrot, diced
• 1 celery stick, chopped
• 2 thyme sprigs
• 1 bay leaf
• 650g sweet potatoes, cut into chunks
• 75ml milk
• 20g butter
• 1 small onion, finely chopped
• 1 garlic clove, crushed
• ½ celery stick, finely sliced
• 1 small carrot, finely chopped
• 500g beef mince, 10% fat
• 3 tbsp tomato & vegetable purée
• 200ml passata
• 50ml milk