Old-school venison pie with juniper, rosemary & bay

INGREDIENTS

• olive oil
• 3 medium red onions, peeled and sliced
• 3 cloves garlic, peeled and chopped
• 2 carrots, peeled and chopped
• 2 sticks celery, trimmed and chopped
• 4 field mushrooms, peeled
• 1 kg quality stewing venison, cut into 2cm cubes
• a few sprigs fresh rosemary, leaves picked and chopped
• a few sprigs fresh thyme, leaves picked
• a few fresh bay leaves
• sea salt
• 1 teaspoon freshly ground black pepper
• 5-6 juniper berries, bashed in a pestle and mortar
• 500 ml ale, preferably Scottish
• 1 heaped tablespoon plain flour
• 350 g ready-made all-butter puff pastry
• 1 large free-range egg, beaten