Preheat oven to 375 degrees F (190 degrees C).

Melt butter in a skillet over medium heat.

Add chopped pecans to the melted butter and cook until lightly browned and fragrant, about 3-5 minutes. Set aside.

Lightly flour a clean surface.

Roll out the puff pastry on the floured surface to slightly larger than the brie round.

Place the brie round in the center of the rolled-out puff pastry.

Top the brie with the browned pecans, brown sugar, and cinnamon.

Gather the edges of the puff pastry around the brie to form a pouch, ensuring the brie is completely enclosed.

Pinch the edges of the pastry together to seal the brie inside.

Tie the top of the pastry pouch with kitchen string to secure the filling.

In a small bowl, whisk an egg with a tablespoon of water to make an egg wash.

Brush the entire surface of the pastry pouch with the egg wash.

Place the puff brie on a baking sheet lined with parchment paper.

Bake in the preheated oven for 20-30 minutes, or until the puff pastry is golden brown and puffed up.

Remove from the oven and let stand for 15 minutes before slicing and serving.