Unfold 1 puff pastry sheet and press into the bottom of a greased pie pan. Cut off extra crust corners. Bake for 10 minutes at 375˚ then remove from oven and let cool. Keep the oven on as you'll bake again with filling, next.
Press the cooled puff pastry down as needed to flat some. Add blueberries on top. Sprinkle sugar evenly over top.
Next, pour lemon juice evenly over top then sprinkle pectin evenly over top of the blueberries. Toss blueberries to coat and spread pectin and lemon. Finally, place darts of butter throughout.
Unfold remaining puff pastry sheet and place on top of the pie, cut off or fold under extra dough. Pinch edges to seal and poke holes with a fork or cut small slits to vent the top.
Optional: Brush top of pie crust with milk then sprinkle with sparkling sugar.
Bake at 375˚ for about 30-35 minutes or until puff pastry becomes light golden brown and filling is bubbling.
The pie will thicken as it cools. If you prefer to eat it warm it may be a little runny.
If the top of the pie starts to brow too early, cover loosely with a piece of foil.You can substitute pectin with quick-cook tapioca to thicken your pie filling.You can use regular pie crust for the top and/or bottom crust if you prefer. Cook time may vary slightly.