Thanks to all who provided advice regarding my giant birthday cake for my Dad's 70th birthday.(and other aspects of the party that is thank god behind us now.)
I used the recipe that I posted in my initial query (from a 1996 Gourmet cover). Made 1 1/2 recipe, baked in 10, 8 and 6 inch pans. Filled w/ choc ganache as per recipe. Froze for one week. All that worked out beautifully. (OK, I accidentally left out 1/2 cup sugar out of 2 1/2 cups...couldn't tell the difference) The layers baked up almost perfectly level even though I couldn't find any Magi-strips. So far so good.
Fri. morning a started the buttercream. As instructed, I had bought a copy of the Cake Bible. Even though I used the recipe from Gourmet, I checked the icing to the Cake Bible and it was more or less the same as Levy's Mousseline Buttercream w/ her recommended variation of adding of fruit curd.
I whipped the egg whites and boiled the sugar syrup. At 248 degrees I started streaming it into the stiff-peaked whites. Everything was fine....and then it turned into a puddle. It had been a long time since I made Italian Meringue (ever since I discovered the hand-mixer in a double boiler method), and I felt I had followed the recipe exactly, but it sure looked like a failure to me. I dumped it out and started over. Consulted Levy and noted that she said to pour the sugar syrup into a glass measure before adding to the whites. Did that the second time and it worked beautifully. Added the butter, and as promised, it looked thin at first, then curdled (the thrilling part), then turned into beautiful, glossy, fluffy but creamy icing. Added the orange curd, zest, a drizzle of Grand Marnier, stuck it in the fridge. Success!
Got up at 6:15 on Sat and took it out of the fridge to come to room temp. At 10:00 started to beat it. Out of fear, I only did 1/2 at a time. It started to break down and formed a small puddle. I consult Levy again. She says if you beat while too cold it can break down "irritrievably" YIKES!! I go do some other errands and come back at noon. Whipped it and it came together and looked great again. Whipped the other half and it behaved nicely. Slapped it on each tier and put the extra icing in a pastry bag.
I transported the tiers to party locale in separate containers. Refrigerated 30 minutes on arrival because the car was warm for the first 5 minutes of the 15 min drive. Stacked the tiers (used the drinking straw trick for support), piped shells to cover the intersection of layers, and decorated with my tiny orange pansies. Left at room temp. This was about 3:30. It looked pretty good if I do say so myself.
At 6:30, with 42 guests crowding into my parent's kitchen (where we had been using two ovens) I lit 6 birthday candles and we sang happy birthday BEFORE starting dinner. Oh, such a good idea on my Mom's part! The cake was beginning to take on an interesting sheen. Like a lady who doesn't sweat, but glows. In a couple of spots I thought I could see choc. cake through the icing.
About 45 minutes later, when I actually cut the cake, icing was sliding off in several places. On the individual plates you couldn't really tell there was a problem, but the icing was really greasier than I would have prefered. If we had waited until then to show off the cake and blow out the candles, I would have been embarrassed.
In the end, we served 42 with the 8 and 10 inch layers with only about 2 hefty pieces left. The 6 inch is in my Dad's fridge untouched, but ruined in my opinion because I don't like chilled cake, however the icing would be on the plate instead of the cake if not.
This recipe is going in the trash. I don't need this kind of grief. The house was not THAT hot. We had the A/C on. Even while piping the icing I had to put the bag back in the fridge for a minute because the heat from my hand was melting it. What if this had been an outside affair? The only significant difference (as far as I can tell) between this recipe and the one in the cake bible is that this one had more butter. I had assumed that would add stiffness and stability, perhaps I was wrong. Do you experienced buttercream-makers run into these problems? BTW, the layers done with the batch of icing that broke down at first behaved exactly the same if not better than the layer w/ the batch that was tempered longer before beating.
Sorry this was so long, but I wanted to give details in case someone wants to take up the case for buttercream and explain the error of my ways before I go back to making nothing but ganache frosting. I'll post a picture if I can figure out how. Thanks!