Preheat the oven to 180°C/350°F/Gas mark 4.
Sauté the onions lightly in the butter until golden. Add the garlic and sauté for a further 1 minute. Sprinkle the game meat with flour, and brown gently in the oil.
Stew the meat slowly in a large covered saucepan with the bacon, onions, garlic, bay leaf, stock and wine. Just before the meat is done, add the mushrooms. Continue cooking until tender. Allow to cool.
Line a small pie dish with the puff pastry, leaving enough to make a lid. Fill with the meat mixture, cover with pastry and seal the edges. Brush with the egg. Bake for 25 minutes or until golden brown. Serve hot.