Chicken, cider and apple casserole

INGREDIENTS

• 2 tbsp flour, seasoned with salt and freshly ground black pepper
• 4 boneless (but not skinless, ideally) chicken breasts
• 3 tbsp light olive oil
• 25g/1oz butter
• 1 large onion
• 1 large carrot
• 2 celery
• ½ tsp finely chopped fresh thyme
• 175ml/6fl oz chicken or vegetable stock
• 175ml/6fl oz dry cider
• 1 large or 2 smaller Blenheim or Cox apples
• salt and freshly ground black pepper