Cherry Pie Filling from Frozen Cherries

I have always made cherry and berry pies with frozen fruit, not precooked, and they always come out runny. This year I decided I would try cooking the cherry filling ahead of time. It was a bit of extra work, but since I had time, it was totally worth it. This resulted the best cherry pie I have ever made.

3 lbs frozen sour cherries, pitted and thawed (retain the juice)
3/4 cup sugar (more if desired)
1/3 cup corn starch

Allow the cherries to thaw completely. Drain off the juice and reserve it.

In a Dutch oven, combine the cherry juice, sugar, and cornstarch. Cook over medium heat, stirring well, until the sugar and cornstarch are totally dissolved and the mixture reduces and thickens substantially. Stir in the cherries and remove from heat.

To make pie, fill pie shell with the mixture and top as desired; bake for 10 minutes at 450 degrees followed by 40-50 more minutes at 350 degrees.

Makes enough for one relatively deep 9-inch pie.