We use all-purpose flour in all our recipes unless otherwise stated. Cake flour is made from soft wheat. It produces a cake with a finer crumb than one made with all-purpose flour. I often use half cake flour and half all-purpose flour in cake recipes. Tapioca flour is great for crisps and pie fillings because it thickens fruit mixtures quickly and produces a translucent sauce. It is available in oriental markets. If you cannot locate it, you can substitute 1 tablespoon all-purpose flour for each 1 teaspoons tapioca flour.