Clarified butter is optional but recommended in a génoise. It gives what is ordinarily a rather plain, somewhat dry sponge an enhanced butter flavor. Of course if you don’t have — or don’t like making — clarified butter, regular melted butter will still produce a excellent result.
This recipe makes enough for one 18″ x 13″ sheet (a jelly roll, bûche de Noël, batch of petits fours) or one 9″ cake. Here’s the formula:
4.5 ounces (1 cup) cake flour
2 ounces (4 tablespoons) butter
½ teaspoon salt
7 ounces (1 cup) sugar
1 teaspoon vanilla extact
Preheat your oven to 350 degrees Fahrenheit.
Set a saucepan big enough to hold your mixer bowl on the stove with an inch of water in it. Bring it to a simmer. Meanwhile, sift the flour and salt together into a medium bowl. Melt the butter in a small saucepan and set aside.
Pour the sugar into the mixer bowl, add the eggs and whisk to combine. Set the mixer bowl over the pan of water and heat the mixture until it’s warm to the touch (no more than 120 degrees). What you’re trying to do is simply melt the sugar…don’t cook the eggs! It’ll only take a minute or so.
Remove the bowl from the heat and, using the paddle attachment, beat the mixture on medium high until it’s very light and foamy, about triple its original volume (this will take up to ten minutes with a stand mixer). Add the vanilla and beat an additional 10-15 seconds.
Pour a cup or so of the egg foam into the cooled melted butter and stir it until it’s completely incorporated, then gently pour the mixture back into the mixer bowl (this eases the incorporation of the butter into the batter). Next, sprinkle the flour mixture into the mixer bowl and carefully fold (instructions under the “Techniques” menu to the right) until the flour mixture and the butter mixture are completely incorporated. Gently pour the batter into the prepared pan.
Bake until the cake is a pale gold color and springs back lightly when touched.