All-purpose flour isn't really made for every purpose. For the best results when baking a cake, you need to use cake flour, a finely milled and typically bleached variety of flour made from soft winter wheat. With a lower content of gluten-producing proteins than in all-purpose flour--around 7 percent versus 10 percent to 12 percent--cake flour yields baked goods with a fine, soft texture. The bleaching process also raises the acidity of the batter, which allows the starch in the flour to absorb more moisture, further enhancing the cake's tenderness. Although cake flour is readily available at grocery stores, in a pinch, you can substitute three-quarters of a cup of all-purpose flour mixed with two tablespoons of cornstarch for each cup of cake flour called for in the recipe.