Whisk together the sugar and cornstarch in a large saucepan. Gradually whisk in the water and lemon juice until smooth.
Add the frozen cherries and place over medium heat.
Cook, stirring frequently, until the cherries thaw and the mixture comes to a simmer.
Continue cooking for 3–5 minutes, stirring gently, until thickened and glossy.
Remove from the heat and transfer to a shallow bowl or baking dish. Cool completely to room temperature.
Stir in the vanilla bean paste once the filling has cooled.
Cover and refrigerate for at least 4 hours, preferably overnight, before using.
Spoon the chilled filling into a prepared 9-inch pie crust, top with a second crust or lattice, and bake according to your preferred pie recipe until the crust is deeply golden and the filling is bubbling.
