If using frozen cherries, make sure they are thawed.
Cook cherries in a saucepan over medium heat until they start to simmer and the juice releases stirring continuously – you don’t want the cherries or sugar to burn. Remove from heat.
In a separate bowl, mix the sugar and cornstarch together. Add the lemon juice. Pour the mixture into the hot cherries and mix thoroughly.
Put the cherry mixture back onto low heat, bring to a simmer once more and keep cooking until the filling has thickened, again stirring often. This should take about 2 minutes.
Remove from heat and let it cool before using.
Pour the cherry pie filling into your prepared pie crust, top with the second crust and crimp the edges.
I would use a pie crust shield to keep the edges from overbrowning.
Place the cherry pie on a baking tray and bake for 20 minutes at 400F
Reduce heat to 375F and then bake for another 30 to 35 minutes. Remove from the oven and let cool.