Mixed game cottage pie - Shooting UK

Ingredients

• 2tbsp duck fat or dripping
• 2 carrots, diced small
• 1 stick celery with strings removed, sliced
• 2 medium onions, finely chopped
• 3 garlic cloves, finely chopped
• 1kg small-diced (1cm pieces) mixed game (venison, wild boar, rabbit, pheasant, mallard)
• 1tsp dried thyme leaves
• 4 juniper berries, crushed
• 1tbsp tomato puree
• 75ml red wine or port
• about 1 ltr beef or chicken stock
• 1 bay leaf
• 2tbsp Worcestershire sauce
• 1.5kg large potatoes, peeled
• 100g butter, melted
• 4 bone marrow rounds, cut to about 8cm in length
• Extra butter for the surface