On a lightly floured surface, roll one half of pie dough to a 1/8-in.-thick circle; transfer to a 9-in. pie plate. Trim pastry even with rim; flute edge. Refrigerate 30 minutes. Leave remaining pie dough refrigerated.
Preheat oven to 205°. Combine blueberries, sugar, tapioca, lemon juice and salt; toss gently. Let stand for 15 minutes.
Add filling to pie pastry; dot with butter. Bake 20 minutes on a lower oven rack. Reduce heat to 175°; bake 10 minutes more. Cover edges loosely with foil to prevent burning. Return to lower rack of oven; bake 15-20 minutes longer, until blueberries are bubbly and beginning to burst. Cool on a wire rack.
Roll remaining dough to a 1/8-in.-thick circle. Cut out stars using different-sized cookie cutters as desired. Place on an ungreased baking sheet. Bake at 175° until golden brown, 5-10 minutes. Remove to wire racks to cool. Place stars over cooled pie in any pattern desired.

For a filling that's ultra smooth, finely grind tapioca in a food processor before stirring it in.

Don't skip the 30-minute resting time before baking: It helps your fluting stay defined.