Preheat oven to 375°F.
Lightly coat a 15 x 11-inch jellyroll pan with cooking spray.
On a lightly floured surface, roll each sheet of puff pastry into a 10 x 12-inch rectangle. Place sheets on pan and press evenly onto the bottom and sides. Trim edges, if needed.
Prick pastry with a fork. Cover with aluminum foil and spread dried beans or pie weights on top. Bake 10 minutes.
Remove from oven, remove beans or pie weights and foil, and reduce oven temperature to 350°F.
In a medium bowl, whisk together sweet potatoes, sugar, cream, eggs, pumpkin pie spice, vanilla and salt until well combined. Pour evenly over crust. Bake 30 minutes.
To make streusel, place cookie crumbs in a bowl. Add butter and cut into crumbswith a fork until mixture resembles cornmeal. Stir in pecans and toffee.
Sprinkle streusel over pie and bake 30 minutes, or until filling is set. Cover pastry edges with foil if needed to prevent overbrowning.
Let cool completely, then refrigerate. Serve chilled with whipped cream.