Roll out one pie crust to fit into pie plate. Roll second pie crust. Place both in fridge to rest at least 30 minutes.
Position rack into lower third of the oven. Preheat to 425°F.
In a medium bowl, toss blueberries with lemon juice.
In a small bowl, mix sugar, cornstarch, salt and cinnamon (if using). Add to blueberries and mix well. Let sit 15 minutes.
Pour blueberry mixture into bottom crust. Scatter butter pieces over blueberry mixture.
Moisten outer edge of bottom crust with cold water. Cover with top crust, pinch edges to seal. Trim crust edges to 1". Moisten underside of edges, fold underneath, pinch to seal. Decorate edges if desired.
If using a closed top crust, cut slits to vent steam.
Place pie on baking sheet to catch drips. Bake 425°F for 30 minutes. Reduce heat to 350°F. Bake an additional 25-35 minutes until thick juices bubble through slits.
Remove from oven and let cool. Store at room temperature up to 1 day. Refrigerate for up to 4 days. Serve warm or cold.