Julie, if I play around with baking powder, is there a formula to follow? This cake is from the RHC Marble Velvet cake and it calls for 2 teaspoons baking powder (don’t have the book with me right now but I think that’s what it is). You think 1 1/2 tsp will work?
Jess, there probably is a formula, and you’d think I would know it- but I don’t. In general, the greater the distance between sides/ the greater the surface area, the lower the amount (butter cakes only). Switching to a smaller pan (like changing a 9x2 layer cake to a loaf or 6C bundt) could mean an increase if you still want a flat top, except that most of the smaller pans look good with rounded tops (cupcakes, loafs).
Matthew says that theory will get you in the right ballpark, but then practice cakes are necessary to fine-tune the formula, and I believe him.
By using the heat core, you have effectively cut the distance between the sides in half, and used a stronger flour, so I wouldn’t add in a third adjustment if you’re happy with the texture.
If you’re feeling ambitious, you could figure out how much baking powder the downy yellow uses per 100g of batter at different pan sizes (using the back of the Cake Bible), and that would give you a starting point.
Julie, that is interesting. I may have to put on my mad scientist hat sometime to play around with this. For now, I think the two adjustments do work. The texture and structure is much, much better than the first test and the result is a cake that I can work on and decorate. I don’t think I’ll do another test cake since I already fed both people in my office and my partner’s office with Marble Cake the last couple of days!