1. Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and line a baking sheet with Gefen Parchment Paper.
2. Finely dice mushroom stems. Combine stems, onion, and meats, and add all seasonings. Stuff mushrooms.
3. Cut the puff pastry into 12 squares (or adjust to the size and quantity of your mushrooms). Wrap each mushroom so the seam is under the bottom of the mushroom cap. Lay them seam-side down on prepared baking sheet.
4. Brush with beaten egg. Bake 30 minutes or until golden brown.