Lisa Ludwinski of Sister Pie in Detroit says this sweet-tart recipe, which she shares in her new Sister Pie cookbook, might be her all-time favorite--especially served with vanilla ice cream. Note: There is a step of blind-baking the crust (par-baking it before filling so that the crust gets nice and crispy). You'll need pie weights or a couple pounds of dried beans.
Not to be confused with tapioca pearls, tapioca flour (sometimes labeled tapioca starch) is powdery like cornstarch. It's a good thickener for pies because it doesn't cloud the filling. Bob's Red Mill is one widely available brand.