Mix the pumpkin purée, brown sugar, pumpkin pie spice, and salt in a bowl for the filling. Set aside.
In a small bowl, whisk an egg for the egg wash.
Roll out a thawed sheet of puff pastry. Cut into even strips and place the pumpkin pie filling down the middle. Take a matching strip and lay over on top. Crimp with a fork and brush with egg wash. Then sprinkle sanding sugar on top.
Bake 12-15 minutes at 400°F or until golden brown.
With a hand mixer, whip the whipping cream, powdered sugar, and vanilla until thick. Use as a dip.