Preheat your oven to 375°F (190°C). Roll out the cold pie crust on a lightly floured surface into a circle slightly larger than your pie dish. Carefully transfer it into the dish, pressing gently to fit the edges. Chill the crust in the fridge while preparing the filling.
In a saucepan, combine the pitted cherries, sugar, and lemon juice. Bring the mixture to a gentle simmer over medium heat, stirring occasionally. Watch as the juices start to bubble and release a sweet aroma.
Sprinkle the cornstarch evenly over the cherries, stirring constantly to prevent lumps. Continue simmering and stirring until the mixture thickens and becomes glossy, about 5-7 minutes. Remove from heat and stir in small pieces of butter until melted and shiny.
Pour the hot cherry filling into the prepared pie crust, spreading it evenly with a spatula. Be cautious of the bubbling hot filling to avoid splashes. Dot the top with additional small pieces of butter if desired for extra gloss.
Brush the edges of the crust with the beaten egg, giving it a shiny, golden finish. Cover the edges with foil or a crust shield to prevent over-browning.
Bake the pie in the preheated oven for about 45 minutes, or until the crust is golden brown and the filling is bubbling at the edges. Check halfway through and cover the edges if they are browning too quickly.
Once baked, remove the pie from the oven and let it cool for at least two hours. This allows the filling to set and makes slicing easier, revealing a vibrant, glossy cherry interior with a crisp, golden crust.
