Roll piecrust to 1/4-inch thickness. Fit into a 10-inch cast-iron skillet. Trim excess pastry along edges, reserving trimmings. Prick bottom and sides of piecrust with a fork.
Bake at 375° for 8 minutes. Remove from oven. Set aside.
Cut butter into flour with a pastry blender until crumbly; add 1/2 cup sugar.
Place one-third of blueberries in piecrust; sprinkle with about one-third remaining sugar. Sprinkle with one-third flour mixture. Top with one-third of pastry trimmings. Repeat layering procedure twice. Sprinkle with additional sugar.
Bake at 375° for 50 minutes or until crust is lightly browned.