If you want to make 3 x 9” round x2” high, the instructions are in the back of The Cake Bible. The white base cake p 491 is the very same cake as the White Velvet in the front of the book. The base is equivalent to one 6"x2” pan. To get a single 9"x2”, you multiply the base ingredient amounts by 4. How do I know that? By looking at the chart on p 490. But the baking powder amounts are in a separate chart p. 492. Take a look. You’ll see that 9-10” cakes need 6.52 grams per base. A 9” cake is 4x base, so multiply 6.52 by 4 = 26 grams baking powder. (Or if you prefer, figure it out in tsp or ounces.)
Believe it or not, this is lots easier to do than multiplying the recipe at the beginning of the book by 1.33, and then trying to figure out the baking powder by guess and by golly! Especially where you want three 9” rounds and not just two. Do the calculations. You’ll be so proud of yourself, and you’ll grow in faith that you can make any size cake you want any time.
The choc base cake is the same as the Perfect All American Choc Cake (not torte!), and the yellow base cake is the same as the All Occasion Downy Yellow. So there you go! You now have enough info to open a bakery. More than one person has done just that!