Begin by preheating your oven to 375°F (190°C) and prepare a baking sheet by lining it with parchment paper.
In a mixing bowl, combine chopped pecans, brown sugar, melted butter, vanilla extract, and salt. Mix until it forms a sticky filling.
Roll out the puff pastry sheet into a rectangular shape on a lightly floured surface.
Spread the pecan filling evenly over the pastry sheet, leaving a border around the edges.
Carefully fold the pastry sheet in half lengthwise to cover the pecan filling.
Use a fork to press down and seal the edges of the braid.
Beat the egg and brush it over the top of the braid for a golden finish.
Bake for 20-25 minutes or until the braid is golden brown and puffed up.
Before slicing and serving allow it to cool for a few minutes.