People, this cake. First, it is completely and totally ridiculous. It has two frostings — two — and one of them is a Swiss buttercream, of all things. It asks you to brown butter and then refrigerate it so you can cream it later. You have to make your own damn caramel. It will take every bowl in your kitchen. But it is so totally worth it.
(Q: Why, Sarah, have we been downgraded to terrible cell phone photos? A: Because my camera had a weird error and it took me two weeks to figure out how to fix it. Better photos are returning to us soon.)
You could definitely make the cakes a day ahead and store them wrapped in plastic, but keeping the frostings at a spreadable temperature is a bit tricky as is — I made this on a hot day and needed to chill them in the fridge — so I wouldn’t recommend making them before the day you plan to frost the cake.
Brown Butter Cake
1 1/2 c. unsalted butter (that’s three sticks or 12 oz.)
1 2/3 c. sugar
2 eggs plus 4 egg yolks (save the whites for the frosting)
2 1/2 c. plus 2 T. flour
3 t. baking powder
1 1/4 c. milk (I used whole)
Put the butter in a saucepan and place it over a burner turned to medium-high. Once the butter is melted, frequently (and carefully!) swirl the pan or stir it with a silicone spatula. It will foam and then boil, and then, after a few minutes, start to turn brown. You want to smell nutty and have a lovely deep golden-brown color. Watch it carefully so it doesn’t burn.
Once the butter is brown, remove the pan from the heat and pour the butter into a heatproof container. (I used a Pyrex bowl. You could also use a baking pan, but not a nonstick one: the boiling butter could damage the coating.) Stick it in the fridge and leave it there for an hour or so, until it resolidifies. During this process the yellow dairy solids will float to the top and the browned bits will sink to the bottom. Do not worry.
Preheat the oven to 350 F and butter and flour two nine-inch round cake pans.
Using a stand or handheld mixer, beat the browned butter until it becomes creamy. Add the sugar and beat for a minute or two until the mixture becomes fluffy.
Add the eggs one at a time, then the yolks two at a time, beating between each addition.
Combine the dry ingredients — flour, baking powder, and salt — in a medium bowl. Add a third of the mix to the butter mixture and stir to combine, then add half of the milk and mix again. Repeat, stirring between each addition, and then add the final third of the flour mixture. If you use the mixer for this, make sure it’s on the lowest setting. Either way, mix just until incorporated.
Divide the batter between the two prepared pans and bake until a toothpick comes out clean, 35-40 minutes.
Let the cakes cool on racks for about half an hour before running a butter knife around the edge and inverting the pans to remove the cakes.
Chocolate Ganache Filling
6 oz. semisweet chocolate
6 T. heavy cream
Break or chop the semisweet chocolate into small pieces. (I recommend using the bar stuff rather than chips, as it sometimes has more fat and thus a smoother feel on the tongue.)
You need to melt the chocolate and cream together gently. The easiest way to do this is in a Pyrex measuring cup in the microwave: start with 30 seconds, then do 15-second increments, stirring between each. Stop when the chocolate is mostly melted and just stir until it fully melts.
The other way to do it is in a double boiler or a metal bowl set over a pan with a couple of inches of simmering water, stirring constantly until it is smooth.
However you choose to do this, you need to then cool the ganache to room temperature or, if it is summer, a little below.
Caramel Buttercream Frosting
1 3/4 c. sugar
1/2 c. heavy cream at room temperature
4 egg whites (the ones you saved earlier, yes?)
1 1/2 c. unsalted butter at room temperature (that’s still 3 sticks and 3/4 lbs.)
Put one cup of sugar into a saucepan. (Cleanup will be easier if it’s a non-stick pan, but it will be easier to tell how it’s caramelizing if you use a shiny silver pan. Your call.) Add enough water to thoroughly dampen it, so it has a texture like wet sand.
Put the saucepan on a burner over medium heat and swirl until the sugar dissolves. Turn the heat up to medium high and keep watching and swirling every few seconds. (Do not stir, as it can let the sugar crystallize, which is bad.) It will bubble and appear to do nothing until you are thoroughly bored. It is trying to lure you to look away so it can burn; do not fall for it. Eventually, it will start to turn golden and then will move very quickly to being a lovely deep caramel color. Take the pan off the heat.
Now you can stir: whisking constantly, pour the cream into the caramel. It will bubble and steam; watch out for steam burns. Set the caramel aside. Resist the urge to taste it unless you like having a burned tongue.
Now, in the top of a double boiler, or a metal bowl set over a few inches of simmering water, combine the egg whites and the remaining 3/4 cup sugar. Whisk them together until the sugar dissolves. (The only reliable way to figure this out that I’ve found is to rub the mix between your index finger and thumb and see if you can feel the grains of sugar.)
You have two choices here. One is that you can take the egg-sugar mix off the heat once the sugar is dissolved. The other is that you can continue heating the mix to 160 degrees on a thermometer, which might not be the worst idea, given all of the salmonella hullabaloo recently.
When you take the egg mix off the heat, put it in a heatproof bowl (if it isn’t already) and mix it on medium. If you heated to 160, you’ll need to beat it for about five minutes to let it cool down so the frosting doesn’t break; you should be able to touch it comfortably. If you didn’t, you can just beat it until it doubles in volume, roughly. It won’t get huge like egg whites alone, but will incorporate some air.
Add the butter half a stick at a time, beating each time until it is incorporated. At this stage, it may well look like a curdled mess. Keep the faith. You will want to beat it for at least five and maybe ten minutes after all the butter is added, and in this time, it will come back together and get very thick and smooth.
After this happens, pour in the caramel (which should still be thickly pourable; if not, warm it slightly on the stove) and beat to combine. If you’re planning to cool the frosting or otherwise keep it before using, cover the surface with plastic wrap so it doesn’t dry out.
Assemble the cake by putting one cake layer on a plate or platter and spreading the ganache over the top. Top this with the second cake layer, and frost the sides and top with the buttercream. If it’s meltingly hot, refrigerate to keep the frosting set.