Tomorrow is the thesis defense of a very special chocoholic, so I made some cake as a sort of pre-celebration treat. The goal was to have layers of chocolate genoise filled with an ultra-decadent bittersweet chocolate mousse, with maybe a few sliced strawberries thrown in for good measure. To do this, I started with a cocoa genoise from Flo Braker, which turned out just perfectly; it baked up with a light and spongy texture that belied its deep chocolate flavor. For the mousse portion, I used Alice Medrich’s Chocolate Velvet Mousse from her book Cocolat. In the recipe, she describes the mousse as being thick enough to slice, which was exactly what I was after. I was hoping for a thickness almost approaching a marquise, so the cake would be extraordinarily rich with chocolate. This is the part where things went a little funky.
Since the mousse recipe made 4 1/2 cups, I decided to halve it, since I figured 2 cups or so would be more than enough to fill a split single-layer genoise. All very well, so I dutifully prepared the mousse as directed. But it certainly seemed incredibly fluffy and not dense at all, not to mention quite a bit more than 2 cups. And there was no way this stuff would be thick enough to slice. Had Alice lied to me?! I held my breath and tried piping it onto the cake, stubbornly averting my eyes as it slowly oozed out from between the layers and the strawberries squirted out onto the plate. I then chilled the mousse in the fridge, waiting patiently. It still did not thicken appreciably. Finally, I froze the mousse and managed to cram it in between the layers as such, where it stayed there long enough for me to speedily fill, cut, and serve. Still, I was certain of Alice’s egregious error and determined to never, ever make one of her mousses again. As we sat and ate, gazing at the smears of mousse which dotted every surface of the kitchen, it hit me. Oh, crap. The mistake was mine. I realized immediately what I’d done. Shame on me for blaming the recipe! What was funny is that it took so freaking long for me to figure this out - I’m not perfect by any means, but for some reason I was certain that I’d followed everything just right…until, ding! Duh.
Trying to fill & slice with room temperature mousse
What happened was this: In my slightly-distracted rushing, I’d screwed up and used half the chocolate but the full amount of everything else. Let this be a lesson to me that when halving recipes, I really ought to write down the halved amounts on a separate sheet of paper, rather than staring at the recipe and trying to reduce everything in my head while I’m also trying to cook it.
Thankfully, the chocolate gods had not abandoned me completely, and the cake tasted great in spite of the snafu. Briefly freezing the filled cake made it easier to cut into slices, and individual slices could be stored in the fridge or freezer for serving. The mousse, while cloudlike and ethereal, was still quite rich with chocolate flavor (if made with twice as much chocolate, as in the original recipe, the stuff would be a force to reckon with indeed). So instead of the rich and dark den of chocolate sin I’d anticipated, my cake was buoyant, creamy, and refreshing, while still holding its own in the chocolate department. Fortunately, the chocoholic also happily approved of this turn of events.
After filling it with partially frozen mousse, then freezing the cake for about 15 minutes to cut into slices (much longer than this and the cake portion would become hard and yucky), it was able to sit at room temperature for about 15-20 minutes or so before the mousse became too soft again and started creeping from the sides of the cake. Even though my luck in fixing kitchen goofs worked out today, I will not try to intentionally screw up that mousse recipe again. :) Still, I will definitely keep the idea of using a particularly light mousse for filling instead of a thick and dense one. If you want to try making a similar cake, below is the recipe for Cocoa Genoise, which was easily one of the best genoises I’ve ever made. Fill it with your own favorite mousse recipe, some sliced fruit if you wish, and dust with confectioner’s sugar.
After freezing for a few minutes - much nicer!
Cocoa Genoise
Adapted from The Simple Art of Perfect Baking by Flo Braker
1/3 cup unsifted cake flour
1/3 cup unsifted cocoa powder
1 tablespoon granulated sugar
2 ounces (4 tablespoons) unsalted butter, melted
3 large eggs, room temperature
2 egg yolks, room temperature
2/3 cup granulated sugar
1 teaspoon vanilla
Preheat oven to 350ºF, position oven rack to lower third of oven.
Grease bottom and sides of a 9-inch springform pan, dust with flour. Place a parchment liner in the bottom of the pan; grease and flour parchment.
Pour flour, cocoa, and 1 tablespoon sugar in that order into a triple sifter. Sift onto a sheet of waxed paper and set aside. Place sugar, eggs, and egg yolks in the bowl of a standing mixer; whisk to combine. Rest the bowl in a shallow skillet filled with one inch of hot (120ºF) tap water. Whisk the egg mixture continuously for about 30 seconds, or until the mixture is around body temperature and when a bit is rubbed between your fingers, it feels smooth, not granular. Don’t let the mixture exceed 110ºF.
Put the bowl on the mixer and whisk on medium speed until the mixture has tripled in volume (3-4 minutes), and it falls in ribbons back to the bowl when the whisk is lifted. Pour in vanilla and beat to combine. With a spatula, sprinkle half of the cocoa-flour mixture on top of the egg mixture and gently fold into the batter. Repeat with the other half of the cocoa-flour mixture, folding just until combined. Pour about 1 cup of the batter into the melted butter and fold until combined. Return the butter mixture to the rest of the batter and gently fold until incorporated, being careful not to deflate the batter.
Gently pour batter into the pan, smoothing the top with a spatula. Bake for 15-27 minutes or until the top springs back slightly when touched and the sides begin to contract from the pan. Cool for 10 minutes, then release sides of springform pan (loosening the sides with knife if necessary). Cool completely.
