Preheat oven to 400 degrees F (200 degrees C). Trim the rind of the Brie Cheese (8 ounce).
Heat a small skillet to medium heat high and add Olive Oil (1 tablespoon). Add Mushroom (1 cup) and season with Salt and Pepper (to taste). Move the mushrooms with a spatula frequently until they have reduced, then lower heat to medium-low.
Add Garlic (1 clove) to the pan and brown with the mushrooms for 2-3 minutes.
Add Marsala Wine (1 tablespoon), and cook until the liquid has evaporated. Once evaporated, transfer to a bowl and set aside.
Lightly dust a cutting board with the All-Purpose Flour (2 tablespoon). Unfold and place Puff Pastry (1 package) on the surface. Place the prepared mushrooms in the center of the pastry and then stack the brie on top of it.
Fold pastry over cheese, trimming the excess. You can use the excess pastry to decorate if you wish.
Whisk Egg (1) and Water (1 tablespoon) to create an egg wash. Lightly coat the pastry seams with egg wash to seal and flip the wrapped brie over so the seam side is down.
Brush egg wash over the entire wrapped Brie. Bake for 25 minutes.
Let stand for 15-20 minutes before serving as the brie will be very hot and viscous. Enjoy!