I made this cake for Denny’s mom’s (aka Nana’s) birthday. It’s just your basic white cake, but I did it using the Cook’s Illustrated technique of baking it in a half-sheet pan and cutting in into quarters for a 4-layer rectangular cake. In this case I’m not 100% sure it was easier than splitting two rounds, because the cake was pretty delicate. It works well with carrot cake, because that seems a little denser and heartier than delicate white cake. I did have a couple of fall-aparty issues, but once everything was glued together with filling and buttercream, it was good.
The raspberry mascarpone filling I just kind of improvised. I think it was about 3/4 cup seedless raspberry jam, melted, that I whipped up with a tub of softened mascarpone cheese. That turned out pretty goopy, so I chilled it until it was firmer, and then I made some lightly sweetened whipped cream and folded them together. Tada! It could have used some lemon juice, but I didn’t have any lemons, so here we are.
The Swiss meringue buttercream was a new adventure for me. I used Smitten Kitchen’s recipe on the recommendation of a friend, and it was really good. The only change I made was I used salted butter instead of unsalted. I liked it, and the people who ate it liked it, but I think next time I would use half salted and half unsalted. I like a little salt kick with my sweet, but this was just a little too salty.
The texture was really good. It was thick and dense and held piping very well, but it was also really easy to spread thinly. I was a little nervous that the recipe wasn’t going to make enough, but I managed to make a really thin crumb coat. An hour in the fridge chilled it to a very firm state, which made the remaining frosting go on like a dream. I even had some left over. If I had filled the cake with the frosting, I might not have had quite enough, but I like a different filling anyway.
Here’s the frosting recipe for my records and anyone else who might be interested.
Swiss Buttercream (aka Swiss meringue buttercream), via Smitten Kitchen
1 cup granulated sugar
4 large egg whites
26 tablespoons unsalted butter (or half salted, half unsalted), softened — that’s 3 sticks + 2 tbsp
1 tsp vanilla
Over a pot of simmering water, whisk the egg whites and sugar in a metal bowl, being sure not to touch the bottom of the bowl to the water. When the egg mixture has reached 160F and you can’t feel any sugar granules between your fingers, put it in the standing mixer and mix it with the whisk attachment until it has doubled in volume and has reached room temperature, about 10 minutes. I actually needed to let mine sit for a few minutes to cool, because it was well-whipped and I was afraid of overbeating it.
Add the vanilla and mix it up, then add the butter, a few tablespoons at a time, until it’s all incorporated. Put it on your cake. It will be fine at room temperature for at least 24 hours. Refrigerating it will make it really hard, so only do that for the crumb coat, and be sure to allow time for the cake to get back to room temperature before serving.
Note: this is not a pure white frosting, due to the butter and the vanilla. Clear vanilla would make a big difference, or you could use almond extract or another clear extract in place of vanilla. It’s pretty white, but more of a natural white than a bleach white.