In a saucepan over medium heat, combine cherries, water, lemon juice, sugar and cornstarch.
Bring to a boil; reduce heat to low and cook, stirring frequently, for about 5-10 minutes. You'll know the filling is done when it is thick, the cherries have released their juices, and the "goo" goes from being an opaque pinkish color to a clear, deep red color.
If using, stir in almond extract. Cool slightly before using as a topping.
