Recipes for butter cakes call for various proportions of materials. Results produced by such variations are discussed briefly on pages 474 to 477. With a fair understanding of the possibilities of substituting one material for another, cake recipes may be varied to make the best use of the materials on hand or to produce the desired result in lightness or richness. Formulas that are good to use as a basis for substitution are given on page 482. Because of the difference in grades of flour, it is difficult to give the exact amount of flour required to produce the best result. Butter cakes include cup cakes, pound cakes, cookies, and wafers. They may be plain or may contain fruit or nuts. Directions for mixing and baking butter cakes are given on pages 478 and 479. Directions for filling the pans are given on page 479.