Sauté the onion and garlic until soft. Chop the mushrooms as fine as possible and add to the onion, season and cook for 20 minutes to remove the moisture. Season and sear the venison in a hotpan and set aside. Roll out the pastry and spread with the mushroom puree. Place on the seared venison and roll up inside the pastry. Egg wash the edge to seal and brush all over for maximum glaze. Score the top with a knife and bake in a hot oven 220ºC for 20/25 minutes. Allow to rest before slicing and serving with spiced red cabbage.