Genoise with Passion Fruit Swiss Meringue Buttercream
Nonstick cooking spray with flour
6 tablespoons unsalted butter
1 teaspoon pure vanilla extract
5 large eggs
1/2 cup plus 2 tablespoons superfine sugar
2/3 cup cake flour, sifted
1/2 cup cornstarch
Passion-Fruit Swiss Meringue Buttercream
Preheat oven to 350 degrees with rack set in the lower third. Spray a 9-by-3-inch round baking pan with nonstick cooking spray; line pan with a parchment paper round and spray again. Set aside.
In a small saucepan, melt butter over medium-high heat until nut-brown in color, about 8 minutes. Remove pan from heat and pour butter into a large bowl, leaving any burned sediment behind; stir in vanilla and keep warm (110 to 120 degrees).
Lightly whisk together eggs and sugar in the bowl of an electric mixer; set mixer over (but not touching) simmering water and heat, whisking constantly, until lukewarm to the touch. Transfer bowl to electric mixer fitted with the whisk attachment and beat on high speed until light, airy, and quadruple in volume, at least 5 minutes. Whisk 1 cup egg mixture into warm melted butter mixture; set aside.
Sift together flour and cornstarch. Gently and quickly fold half the flour mixture into remaining egg mixture until all the flour is absorbed. Repeat process with remaining flour mixture. Fold in butter mixture to combine and transfer to prepared baking pan.
Transfer pan to oven and bake until golden brown and starts to shrink slightly from the sides of the pan, 20 to 30 minutes. If possible, avoid opening the oven door until cake has baked at least 30 minutes, as cake is fragile and may fall. Remove cake from oven and unmold immediately onto a wire rack to cool. Let cool completely before cutting into layers and frosting with buttercream.