In a large saucepan combine the frozen cherries, spiced rum, 1 cup water, granulated sugar, vanilla, and salt. Over medium high heat bring the pie filling to a boil. Reduce the heat to medium and stirring regularly let the pie filling boil for 30 minutes. At the beginning the pie filling will boil very rapidly when you stir it. This is the alcohol that is cooking off, and the rapid boiling will stop when the pie filling begins to thicken.
After 30 minutes remove the pie filling from heat. In a small bowl stir together the cornstarch and 1 tablespoon of water. Pour the cornstarch mixture into the pie filling and stir until the mixture is fully combined into the pie filling. You will notice that the filling will start to thicken slightly. Return the pie filling to medium heat and bring the filling to a boil again. Stirring regularly, let the pie filling boil for another 15 minutes.
Remove pie filling from heat and let cool completely.
Preheat oven to 400°F
For the pie crust I highly recommend using my Sweet Dough Pie Crust. Roll out your bottom pie crust and place in your pie plate. Poke the pie crust with a fork a few times just to ensure no bubbles will form.
Pour all the cherry rum pie filling into the pie crust and top with the top crust. To adhere the two crusts together, brush the edges with a little bit of water and pinch. Cut slits in the top of the pie crust to let the air escape while it is baking.
Brush the top of the pie with the melted butter and sprinkle the entire top of the pie with the cinnamon sugar.
Bake for 25 minutes, then decrease the heat of the oven to 350°F and continue to bake for 35 more minutes.
Let cool at least 30 minutes before serving.