Preheat oven to 400F. Place 12 unbaked tart shells on baking sheet. Bake for 10-12 minutes or until light golden. Remove from oven.
In a small bowl, whisk tapioca starch and water together. Set aside.
In a medium-sized pot, over medium heat, place 1/2 cup blueberries, all the juice and all the sugar. Mix gently and bring to a boil, stirring constantly.
While whisking vigorously, add tapioca mixture. Add vanilla and lemon zest, stirring quickly to blend. Continue to cook while constantly whisking, until the mixture is very thick and glossy, about 2 minutes. Remove from heat. Quickly fold in the balance of the wild blueberries (2 cups).