Combine cherries, sugar, and lemon juice in a bowl and stir to combine.
Mash slightly.
Let sit for 10 minutes.
Pour cherry mixture into sauce pan and bring to boil, stirring frequently over medium heat.
Lower heat to medium low and continue to cook, mashing and stirring, for 5 minutes.
Stir in one tablespoon of cornstarch.
Continue cooking and mashing for another 5 minutes.
Remove from stove and allow to cool.
Notes
Frozen cherries can be used, about 14 ounces since they are already pitted. Be sure to thaw completely.
Sauce can be pureed if a smoother sauce is desired.