Mix together the pitted cherries, sugar, and cornstarch in a bowl and let it sit for ten minutes or so until they get juicy.
Put all ingredients except butter in a heavy pot over medium heat and bring to a boil Bring to a boil. Lower heat and simmer over medium heat, stirring constantly, for several minutes. Stir in the butter.
Let the mixture cool a bit, then pour into pie shells.
This would also be fine over ice cream.