Unfold 1 puff pastry sheet and press into the bottom of a greased pie pan. Cut off extra crust corners.
Pour blueberries into crust. Sprinkle sugar evenly over top. Add more or less to your desired level of sweetness.
Next sprinkle lemon juice evenly over top. Then, if you want a thicker gel-like filling, loosely sprinkle pectin evenly over top of the blueberries. Toss blueberries to coat and spread pectin. 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 to vent the top.
Bake at 375˚ for about 30-35 minutes or until puff pastry becomes light golden brown.
The pie will thicken as it cools due to the natural pectin found in the blueberries. If you prefer to eat it warm it will be a little runny. I personally don't mind this but if you like your pie warm and don't like it runny, then try adding pectin per the packaged instructions.
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.