Chiffon cakes are usually baked in a tube pan like an angel food cake, to support the egg-foam cake as it bakes keeping the center from falling. To bake this one as a layer cake, Rose switched to unbleached all-purpose flour, then adds a rose nail to the center of the pan to help with the heat distribution there. Except I forgot about using the AP flour and just turned back to the recipe for the Bostini, and made it with all cake flour.
I was probably saved by having done a half-recipe, so my cake was only 6 inches across and seemed to hold up fine during baking. I did add the rose nail, too, in the center of the little pan. The center of the cake rose just above the level of the 6" x 3" pan I used (purchased for the upcoming Miette's Tomboy cake)--I have a 6" springform, but it's not as tall as the 3" high cake pan. What did happen was not any dipping of the cake during baking--it had a nice dome. There was some sinking during cooling which, because the cake cools upside down in its pan, showed up as a concave bottom to the cake. Maybe the AP flour would have helped after all.
I also should have waited to see if my cake would sink a little to drop the top of the cake below the pan before upending it for cooling. I did think about it, but decided the cake wasn't that high...but was wrong. So a little of the top crust stuck to my greased cake rack, and the top of my cake looked patchy. I might have just served it upside down but for the concave bottom.
My other mistake with this cake was using the Seville orange marmalade that was already on hand to make orange marmalade whipped cream, when Rose specifies sweet orange marmalade. My cake testers (except for sister-in-law, who really likes less-sweet stuff) panned the cream, calling it "weird" or just saying they didn't like it. Personally I thought it was fine, but there was a different taste balance in there. I added a little sugar to the leftovers and found that improved things.
Overall, the cake was good. I enjoyed it, finding it nicely flavored and well balanced with the orange whipped cream, and I'd make this again as a light dessert to a party. My other tasters thought the cake was OK but not something they particularly enjoyed.