2 8-ounce (225-gram) boxes stuffing mushrooms, stems removed and reserved

1 small white onion, finely diced

1 pound (1/2 kilogram) ground beef

1 6-ounce (170-gram) package pastrami, finely diced

2 teaspoons mushroom soup mix

1 teaspoon dried parsley, such as Gefen

2 cloves garlic, minced or 2 cubes Gefen Frozen Garlic

2 teaspoons paprika

2 teaspoons onion powder

1/4 teaspoon pepper

1 teaspoon salt

1 21-ounce (595-gram) package Gefen Puff Pastry Sheets

1 egg, beaten