Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius). Line a baking sheet with Gefen Parchment Paper.

Place beef, egg, onion, parsley, and salt in a medium bowl. Wet the slice of bread, squeeze out, then chop finely and add to bowl. Mix just to combine.

Cut each puff pastry sheet into 12 squares. Scoop out the meat in tablespoons and form into meatballs. Stretch each puff pastry square out, then place a few pieces of pastrami in the center with a meatball on top. Wrap the puff pastry around the meatball and pinch closed, forming a closed ball. Place seam side down on the prepared baking sheet. Continue with the remaining meatballs. (You should have 20-24 in total.)

Brush your Wellingtons with egg wash and bake for about 40 minutes, or until lightly browned.

Combine sauce ingredients in a small saucepan and bring to a simmer over medium-low heat. Allow to reduce until the alcohol from the bourbon cooks out and the mixture easily coats the back of a spoon, about 10–15 minutes.

Plate two Wellingtons and drizzle with sauce.