In an effort to make a cake but not eat tons of it myself, last weekend I attempted to convert Woody’s Lemon Luxury Layer Cake from RHC from the two 9x2” round cake pans to two 6x2” round cake pans.  This was my first time trying to change cake pans.  I tried putting off the actual converting of the ingredients by reading and reading from this forum, TCB, and RHC for a couple of HOURS.  Needless to say, I was overthinking and second guessing everything. When I thought I got it, I did the conversions and made the cake.  First, I should say that I have never made this cake before, but I have made the Golden Luxury Butter Cake from TCB which is similar with great success and one of my favorites. I also weigh everything and use the correct temperature of the eggs and butter.

I ended up with many issues.  First, it took way too long for the cakes to finish baking (used conventional; should I be using convection from your experience?). At 20 minutes, I started checking the temperature trying to get to 190 degrees F.  I rotated the pans a couple of times from this point on hoping it would help, but checked every 2-5 minutes on the temperature, which I know was bad for letting the hot air out of the oven.  It took 37 minutes total for one pan and 42 minutes for the other.  Second, the layers were tiny, maybe a 1/2” at the most, so there would be no splitting those suckers in half.  Third, I flipped them out and knew I had a bigger problem than I thought; the cake was crumbly and coming apart.  The parchment was difficult to remove without taking off a good amount of cake with it.

I did not finish making the cake since I knew it was messed up.  I was going to attempt it again, but my husband wanted to spend time with me instead of me being in the kitchen all night. 

I really want to try to make this cake and other cakes with 6” pans, but I need to get this figured out first.  One thing is that I’m pretty sure I screwed up the baking powder, but I’ll get to that in a minute.  Here is what I did:
- took volume of pans (p.455 TCB): 6x2” = 3 3/4 cups X 2 = 7 1/2 cups
                      9x2” = 8 2/3 cups x 2 = 17 1/3 cups
- divided the volumes: 7.5/17.3334 = .43269 for my factor
- multiplied .43269 by all cake ingredients, except bp
- for baking powder (p.492 TCB): I saw that I would be going from “Level 2” to “Level 1”. I took 7.35g-6.52g=.83g, then did .83g x 2=1.66g which is the Rose Factor (2) on p. 490; I then took 1.66g/4.9g=.338g to see the amount of bp I needed to add to the listed amount (4.9g bp=1tsp), so I used 4 1/4 tsp. plus an extra 1/3 tsp. bp
      I think one of my mistakes was that I should have taken the 4 1/4 tsp x .43269= 1.83 tsp or 4 1/4 x 4.9g=20.825g x .43269= 9.01g baking powder and then added an additional 1/3 tsp. Correct or totally offbase?

I would appreciate any and all help. If you need more information, photos, or the calculated individual ingredients, I can post that as well.  Thank you!

avivaleah, it sounds like your cake fell because of overleavening and to a lesser extent, underbaking.

Your conversion factor looks fine (about 43%).  If it makes things easier, you can always make half and bake a cupcake or two .

I think you’re right that the oven was open too many times, so that cake may have had effects from being baked in a too-cool oven.  I’ve noticed once or twice that even if you bake to the right internal temp, if the oven is too cool and it takes longer than the specified time the cake can suffer.

Re: the baking powder, the easiest route to go is to just apply the same 43% factor to that, and then trim the tops if they are too rounded.  So that would have been 0.43 x 4.25 = 1.83 tsp.  At this point, I probably would have rounded up to 1 7/8 tsp or at most 2 tsp (rounding up since it makes sense to increase bp a bit when going to a smaller pan).  Your cake was definitely over-leavened if you used 4+ tsp baking powder.  The leavening weakens structure, so it caused the cake to fall.  This would explain both the extreme tenderness and the flat layer.

The way to approach the Rose Factor chart, if you want to go that route, is to remember that those values only work for the downy yellow, white velvet and all-american chocolate.  You can use it to estimate changes in bp for other butter cakes, but the key is to apply a percentage change, not the absolute amount. 

That calculation goes something like this:

-First, multiply the bp by 43% to keep it in line with the other ingredients, which gives 1.83tsp.

-Second, figure out the percentage change from one level to the next in the Rose Factor charts (percentage change per base recipe).  On p. 492, to go from a level two to a level one cake, the baking powder increases from 1.33 tsp to 1.5 tsp, or 12.5%.  So to increase the bp by 12.5%, 1.125 x 1.83 =2.06 tsp.  So 2 tsp would have been the place to start.  But keep in mind that this is theoretical, not tested, so may not be perfect.  It’s probably better to err on the side of too little bp, as it’s easier to trim the tops of the cakes than it is to deal with a fallen cake.

Wow, great explanation, Julie!!!!

great work!  I simply divide everything in half.  u will obtain two 6” cakes near 2” tall each.

Thank you for the detailed explanation.  It helps a lot and makes me feel like I didn’t totally mess up, mainly just the baking powder.

I like the idea of just doing 50% of the ingredients and possibly taking some out to make a cupcake or two.  I would be a little worried about getting the proper amount of batter in the cake pans though.

I hope to make a 6” cake soon!