Golden veggie shepherds pie

Name: Golden veggie shepherd’s pie
Ingredients: 50g butter; 2 onion, chopped; 4 carrot, diced; 1 head of celery, chopped; 4 garlic clove, finely chopped; 200g pack chestnut mushroom, sliced; 2 bay leaf; 1 tbsp dried thyme; 500g pack dried green lentil (we used Merchant Gourmet Puy lentils); 100ml red wine (optional); 1.7l vegetable stock; 3 tbsp tomato purée; 2kg floury potato, such as King Edwards; 85g butter; 100ml milk; 50g cheddar, grated