Position oven rack to lower 1/3 of oven and place a lined baking sheet on the rack. Preheat oven to 400 degrees F.
Roll out 1 disc of pie dough to fit 9 to 9 ½" pie plate with plenty of dough to come up and over sides of pan. Once lined with the dough place the pie plate in the fridge while you prepare the filling.
Combine the blueberries, sugar* (see notes), cornstarch, lemon zest, cinnamon and salt in a large bowl and toss to combine. Pour blueberries into prepared pie pan and place back in fridge while you roll out the second disc of pie dough.
Prepare your top pie dough - making sure you leave some holes for steam to release. If doing a lattice top, see notes in blog post about how to do this.
Combine the egg yolk and heavy cream in a small dish and use a pastry brush to brush the top of the pie crust once it's been placed over the pie filling. Sprinkle the crust with sugar. Use the tablespoon of butter to dot any opening of the pie filling.
Bake the pie on the lined baking sheet at 400 degrees for 20 minutes. Without opening the oven, reduce the heat to 350 degrees F and continue baking for 35 to 45 more minutes, or until the pie filling is bubbling throughout the pie and the top is golden brown.
Remove from oven and let rest for 3 hours, or until cooled. Cover loosely and store at room temperature for up to 2 days, or refrigerate up to 4 days. Enjoy!
* Taste the blueberries for sweetness. If they are tart, add up to 1/4 cup more sugar. If they are really sweet, feel free to reduce the sugar amount slightly. **If using frozen blueberries - make sure to defrost the blueberries first then drain as much excess liquid from them as possible. ***Since all pie plates are different, please cook the pie until the blueberry pie filling is bubbling throughout. This will be a good indicator to know when YOUR pie is done.