Sauté finely chopped onion and bacon in a little oil. Add sliced mushrooms and egg. Finally, add crumbled Niva cheese and chopped chives. Season with salt and black pepper and let it cool. Meanwhile, roll out the puff pastry, evenly layer the cooled filling on it, and roll up. Brush with egg and don’t forget to prick. Bake at 200°C for about 20 minutes.