In a medium sauce pan, add the blueberries, lemon juice, zest, thyme, sugar, and water and stir to combine. Bring the mixture to a boil on medium-high heat. When the liquid is boiling, reduce the heat to a low boil and stir frequently until the liquid begins to evaporate, approximately 20 minutes. Remove 1 cup of the filling with a measuring cup and add the starch to the cup. Whisk until the starch completely dissolves. You shouldn’t see any lumps. Add the mixture back to the pan and stir well. Cook for another 15 minutes and remove from heat. Let cool then refrigerate for at least an hour.