Have your pie dough already prepared into two discs and keep them chilled in the refrigerator before proceeding.
Halve the pitted cherries and quarter any that are soft and overly ripe.
Gently mix the cherries, cornstarch, brown and granulated sugars, salt, lemon and vanilla together. Continue to stir and fold until well mixed, taking care not to mash the cherries.** Allow the mixture to sit room temperature while you roll out the bottom pie pastry - this will allow time for the flavors to meld and for the natural juices to release.
Remove one pie pastry from the refrigerator and allow it to sit undisturbed for 2-3 minutes before rolling it out. Lightly dust a work surface and rolling pin with flour. Roll the pastry out large enough to line a pie pan with about an inch or two overhang. Gently press the pastry into the pan without stretching it. Randomly prick the bottom of the pastry with the tines of a fork to allow for steam to release during baking. Evenly sprinkle the pastry bottom with granulated sugar to help make a light barrier, abut ½ teaspoon.
Using a slotted spoon, add the cherries to the pie pan. Don't discard the juices remaining in the bowl, we'll reduce that. TIP: Allow the excess juice to spill through the slotted spoon, however keep in mind you also want to add some juices to the pie, so don't worry about removing all the juice in each spoonful, just the immediate excess that spills out quickly.
In a medium saucepan over low-medium heat, add 1/4 cup of the reserved juices. Reduce until slightly thick, but still pourable, about 2 minutes. You'll know it's the right consistency when you run a wooden spoon or spatula through the mixture and it briefly stays separated before slowly running back together.
Pour the reduced mixture over the cherries, gently lifting and mixing, as best as possible.
Dot with 1 tablespoon cubed and cold butter. Place the pie in the refrigerator as you roll out the second dough. If you'd like to make a lattice, see the link in notes first for a how-to guide.
Allow the pie pastry to sit undisturbed for 3-4 minutes before rolling it out about 1-2 inches larger than the pie pan. Add it to the pie in either a lattice style or by adding as-is, crimping and folding the edges together and making a few slits on top to release the steam. Place the pie back in the refrigerator while the oven preheats.
Place an empty baking sheet on the lowest tier of the oven and preheat to 400 F.
Right before baking, beat an egg yolk with 1 tablespoon of milk or fresh water to make an egg wash. Lightly brush a thin layer on the top of the pie. Sprinkle with coarse sugar, if desired.
Bake on the baking sheet for 20 minutes, then reduce the temperature to 375 F. for an additional 30-40 minutes, or until deeply golden. Taking care to not let the edges burn, use foil if needed to cover the edges.
The hardest part is letting it rest at least 4 hours before slicing. The contents need to set before serving. Consider serving with a generous scoop of vanilla ice cream.
Notes
MAKING A LATTICE:Our good friends from Serious Eats have a wonderful how-to guide to help you create a beautiful lattice pie crust --> How to Weave a Lattice PieOTHER HELPFUL TIPS:** Taste the cherry mixture and add more sugar before adding to the pie. You might need between 2/3 - 3/4 cup total sugars depending on the sweetness of the cherries, adjust accordingly.Keeping a cold pastry is critical for a pie that won't slip while baking. Work swiftly to ensure a chilled pie crust. Use the refrigerator in intervals while preparing the pie to keep the pastry chilled, if need be. Keep the pie in the refrigerator for an additional 10-15 minutes after the oven has preheated to ensure an adequate chill before baking.