Genoise with French Buttercream Recipe

How to make it

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• Preheat oven to 375. Grease and flour a 10-inch springform pan, cut a circle of parchment paper to fit the bottom and insert it, then grease and flour the parchment paper.
• Heat a pan of water to simmering (I have a water bath attachment on my kitchenaid, so I can just add boiling water to it and let it go, but most don't). Crack the eggs into a mixing bowl, add the sugar and vanilla, place it over the water, and whisk rapidly until the eggs are hot and frothy. Remove from the water bath and put under the mixer. With a whisk attachment, beat the eggs until almost tripled in volume, lemon yellow in color, thick and ribbony.
• While the eggs are beating, sift the flour into a bowl. Add the salt to the flour, and sift it a second time. If you're making a chocolate genoise, sift the cocoa separately, then sift it together with the flour and the salt.
• You're going to fold the flour and butter into the beaten egg mixture. I know this is going to gross some people out, but by far the best tool for folding is your hand, not a spatula. You can feel with your hand; you can't feel with a spatula. Sprinkle about a third of the sifted flour mixture over the eggs, and very quickly but gently, fold it in just until mixed and you can no longer feel bits of flour, using circular motions all the way to the bottom of the bowl, and losing as little air as possible. Repeat twice. Quickly and gently, fold in the melted butter.
• Pour into the springform, smooth the top, and bake for 20-30 minutes, until a toothpick comes out clean. As soon as you remove the cake from the oven, put it on a rack and remove the sides of the pan. Let it cool for 20 minutes, then remove the bottom and the parchment. Let cool completely before working with it.
• The traditional filling is a French buttercream, but you can fill it with anything you like. Because the genoise is dry and relatively firm, it is easy to split. If you don't have a lot of experience splitting cake layers, first split it in half with a sharp serrated knife (tips below), then split each half in halves.
• To split a cake, place the knife in the center along one edge and gently slice about two inches into it. Now, leave the knife stationary, and rotate the cake, not the knife, slicing with the knife as you rotate. When you've returned to where you began, gently move the knife through the center. I use my lazy susan almost exclusively for splitting layers.
• Make the buttercream. Put the egg yolks in a mixing bowl and place over hot water. Whisk until the yolks are hot to the touch. Remove and put under the mixer. Beat at high speed until the yolks have doubled in volume, are lemon yellow, and leave a "ribbon" when you dribble them with a spoon.
• Put the sugar and water in a heavy pan and cook over medium heat, stirring the sides down only until all the sugar is dissolved, until the syrup reaches 250.
• With the mixer on high, very slowly add the syrup to the yolks, until all has been added. Continue beating on high until the mixture is ROOM TEMPERATURE. Still on high, beat in the soft, room temperature butter a tablespoon at a time, then refrigerate for an hour. (If using either flavoring, beat in just after you beat in the butter). Refrigerate the buttercream for at least a half hour, and whip it smooth just before you use it.
• To assemble, place the first layer, cut side up, on the serving plate. Brush all loose crumbs from the top and sides. Sprinkle the top with either thin sugar syrup or some sort of spirits (Grand Marnier, kirsch, etc.) then spread first with a thin layer of buttercream only to about a half inch of the edge. Spread with more buttercream, then repeat with each layer until you place the last on top.
• Spread a very thin layer of buttercream around the sides and over the top. Coat with the remaining buttercream. Coat the sides if you like with something like ground toasted nuts, or dust the top with cocoa. If you have enough buttercream, you can pipe rosettes on the top. You can add strawberry halves or cherry halves to the top. Anything you like.