Preheat oven to 400°. Spray baking sheet with nonstick spray. Roll out thawed (but still cold) puff pastry sheet to get rid of any crease marks or holes.
Assembly
Spread peach butter in the center of the puff pastry, about the size of the brie round.
Add brown sugar then spread pecans on top of peaches. Sit brie onto pecans. Gently (but tightly) fold the puff pastry up and over brie in the center, starting in one corner and working your way around clockwise. Make sure to layer the puff pastry in a way that leaves no holes. Pinch to seal. Carefully flip the entire pastry over and place on prepared baking sheet. Combine egg with about 1tsp of water and whisk to make an egg wash. Brush over the top and sides of puff pastry.
Baking
Bake at 400° for 20-25 minutes. Let it rest for 15-20 minutes before serving. Pair with your favorite baguettes or crackers.
Notes
Feel free to substitute the peach marmalade for fresh peaches or another fruit jam of your choice. Keep in mind that fresh fruits (particularly berries) will add additional liquid to your pastry and may affect bake time and final texture.
Rolling out the puff pastry is only to increase the area available to cover the brie. If your brie is small enough to be wrapped sufficiently, rolling out the puff pastry is a step that can be skipped.