Blend 1 onion, 4-5 cloves of garlic, 2 tbsp soya sauce, 1 tbsp vinegar, ½ cup mushrooms, ½ tsp crushed black pepper, salt to taste and 2 tbsp butter in a blender.
Heat 1 tsp oil in a pan and fry the blended mixture for 5-10 minutes. Then set it aside to cool. Flatten the puff pastry dough.
Marinate ½ kg beef in the mixture and leave it for half an hour. Put beef on the puff pastry dough and add the remaining mixture on the top. Brush 2 eggs on the edges of the puff pastry and roll the dough over the beef.
Pre-heat oven 200c for 40-45 min and bake the puff pastry. Keep on brushing eggs on the puff pastry while baking. Slice and serve it when baked.