Lemon Layer Cake

We had a birthday in the house this week, and birthdays call for layer cake. I made this one with fresh lemons from the tree in our yard.

For the cake layers I made the Whole Wheat Genoise from the King Arthur Flour Whole Grain Baking book. The only change I made to the recipe was to blend a about 2 TBSP of fresh lemon zest with the melted butter before adding that to the cake. This recipe made a generous amount of batter. So generous it was almost too much for my mixer bowl. If I make this again (and I probably will) I'll adjust the quantity downward by about 20-25%. Other future changes include adding lemon extract, which I would have used  had I remembered to buy some). With just lemon zest the citrus flavor of the layers was not as pronounced as I would have liked.

This genoise is the basis for Daffodil Cake on page 404 of the cookbook. I glanced at that recipe but planned to use other sources for the lemon filling and buttercream parts, so didn't study the details. Now I wish I'd read the bit where they recommend soaking each cake layer with 1/4 cup of citrus syrup, which seems like a lot. I thought I'd drenched generously, but probably only used at most half that amount per layer and yes, the final result is a little dry. Not a problem if the cake is served with lots of icecream, but next time around I'll drench more thoroughly.

Overall, I'm impressed by any genoise that can handle 1-3/4 C of whole wheat flour, even if it's ww pastry flour. This did turn out well, and managed to not have the overly eggy flavor of the last genoise I made. It is a little denser than a white flour genoise: it does not slice as cleanly and should be flavored more aggressively.

I cooked the genoise in two 8" round pans (rather than the three pans the recipe calls for), so they came out about 2" thick each. I then sliced each into two layers, to make four total.

For between-layer filling I started with a half recipe of Master Lemon Curd from this reliable book (made a couple of days ahead).

I did not bother to strain the curd as recommended, because I felt leaving the little bits of lemon zest in there would improve the flavor and I knew no one eating the cake would notice or object to the zesty bits. The lemony-ness of the curd improved noticeably from the make-ahead date to the time the cake was assembled, so advance prep is not only convenient, it resulted in a better flavor, too.

When I was ready to fill and frost the layers I turned the lemon curd into a mousse by first soaking 1 tsp of powdered gelatin in 2T of lemon juice mixed with water. The next step with gelatin (after soaking in cold liquid) is to heat and dissolve, which I accomplished by pouring in a little bit of the hot lemon syrup I boiled up for the Italian Meringue Buttercream frosting (more on that, below). I stirred the warmed gelatin into the lemon curd, then used a whisk to fold in some of the (extra) meringue I'd made for the frosting. Mousse typically also includes a fair amount of whipped cream, but I left that out as unnecessary excess and well over the line into just-too-much-more-work land. I chilled the mousse until it had started to set, then spread some over each of three cake layers and chilled the layers until the mousse was fully set before assembling the final cake.

This lemon mouse made a not-too-heavy but very stable cake filling that did not squish out the sides even under the weight of multiple whole wheat genoise layers. I will definitely use it again, and look forward to experimenting with other flavors.

The final piece of this effort was a lemon frosting which was close to a disaster. I have not attempted a classic Italian merinque buttercream in many years and thought I'd give it a go. As mentioned above, I made extra (2 add'l egg whites) of the meringue so I could use some for the lemon filling. The meringue turned out perfectly! I've used my stand mixer to whip egg whites before, but this was the first time I'd done a hot sugar syrup meringue with it, and the results were awesome, huge, voluminos peaks of fluffy but exceptionally stable sweet lemony whiteness.

Unfortunately, that's where the success ended. Adding the butter sort of seemed to go okay: the whites did not curdle, and remained a smooth emulsion, but the loss of volume seemed way beyond what it should have been, and the result, while not the "soupy" texture threatened by too-soft butter, was not stiff enough to frost with. So I stuck it in the fridge to chill up a bit.

In hindsight, I can see that's where I went wrong. I should have put the bowl of not-stiff-enough into an icewater bath while continuing to beat with my hand mixer as it firmed up. Left to its own devices in the fridge a horrible separation of liquid into the bottom of the bowl occured. This appeared to be way, way, way beyond the "curdled" effect that buttercream troubleshooting tips say can be saved, and I was running out of patience, so I drained off the liquid and beat in another stick of butter and some confectioner's sugar.

At that point it was still a bit soft but I could see it would be way too much quantity by the time I got it to a spreadable consistency, so I removed half of what was in the bowl to a freezer container for some future use. To the remaining portion I mixed in a quickie white chocolate ganache I made by melting a bag of white choc chips in some heavy cream. I have great faith in the firm-up potential of ganache and it did chill up beautifully. The final result -- half failed lemon buttercream and half white choc ganache -- handled extremely well, did not sag or droop or end up in a pool on the cake platter, and tasted divine, with an exceptionally smooth texture and a lovely subtle flavor hinting of vanilla, white chocolate (which can be too cloying on its own), and lemon with no one element dominating. Too bad this exact frosting will never be duplicated, as it is well worth eating again and again, but that's what usually happens when I cook.

Although I will do some things differently next time I make a lemon layer cake (which will not be for a good long while, layer cakes being way too much work for anything other than special occasions, although they can be a fun way to make a mess of the kitchen), this was a delicious cake and we ate a lot of it. Leftovers have been divvied up into more reasonable portions and frozen for future cake night indulgence.