Golden veggie shepherd’s pie

Name: Golden veggie shepherd’s pie
Prep time: 30 min
Cook time: 1 h 45 min
Total time: 2 h 15 min
Cuisine: European, British
Ingredients: 50g butter; 2 onions, chopped; 4 carrots, diced; 1 head of celery, chopped; 4 garlic cloves, finely chopped; 200g pack chestnut mushrooms, sliced; 2 bay leaves; 1 tbsp dried thyme; 500g pack dried green lentils (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