From Jacques Torres' "Dessert Circus"
A Bûche de Noël, or Yule Log, is a French Christmas tradition that is now popular in American celebrations. In France, it was typically enjoyed at the end of a large, late supper called le réveillion, which is served after mass on Christmas.
Every Christmas, no matter how busy he is, Jacques always finds the time to make a buche or two to include in his own holiday celebrations. This basic chocolate sponge cake, or génoise, recipe is used to make the Bûche de Noël.
Adapted from Jacques Torres’ “A Year in Chocolate."
Preheat the oven to 425 degrees. Line a 15½-by-10½-by-1-inch baking sheet (jelly roll or quarter sheet pan) with parchment paper.
In the bowl of a stand mixer fitted with the whip, combine the whole eggs, egg yolks, 1/3 cup of the sugar, and the milk and beat on medium-high speed for about 6 minutes, or until the mixture is very light and has tripled in volume.
Place the egg whites in a bowl and, using a handheld mixer, whip on medium speed until foamy. (If you are lucky enough to have 2 bowls for your stand mixer, use a clean one and wash and dry the whip before using it for the egg whites. If not, the whites can be whipped with a handheld mixer or, if you want a workout, a wire whisk). Add the remaining 2 tablespoons sugar a tablespoon at a time and continue to beat. When the sugar has been incorporated, raise the speed to medium-high and whip for about 5 minutes, or until stiff, but not dry, peaks form.
Using a rubber spatula, gently fold about half of the whole egg mixture into the egg whites. When almost incorporated, fold in the remaining half, taking care not to deflate the batter.
Place the flour in a fine-mesh sieve and, tapping on the side of the sieve, sift the flour over the meringue batter. Using a rubber spatula, gently fold the flour into the batter, making sure the spatula reaches to the bottom of the bowl to ensure an even mixture.
Scrape the batter into the prepared pan, and use an offset spatula to spread it evenly. Don’t press down too hard, or the pressure will cause the batter to deflate.
Place the confectioners’ sugar in a fine-mesh sieve and, tapping on the side of the sieve, sift the sugar evenly over the surface of the batter.
Bake for about 5 minutes, or until the cake just begins to brown on the edges. (The short, hot baking period allows the cake to retain its moisture, which will make it easier to roll). Remove from the oven and immediately run a paring knife around the inside edge of the pan to loosen the cake sides. Place a sheet of parchment paper over the top of the cake, and then invert a cookie sheet over the parchment. Immediately invert the cake and the cookie sheet together, then lift off the baking sheet. Peel the parchment paper off the cake. Let cool completely.
Line another cookie sheet with parchment paper. Place the cake on a clean, flat work surface with a long side facing you. Drizzle the simple syrup evenly over the cake, using just enough to moisten but not soak the cake. Spoon the pastry cream on top of the cake and, using an offset spatula, carefully spread the cream evenly over the cake, taking care to spread it evenly up to the edges. Starting at the long end farthest from you, slip your fingers between the parchment and the cake and begin rolling the cake toward you, up and over the pastry cream, until you have a firm long shape, or roulade.
Carefully transfer the roulade, seam side down, to the prepared cookie sheet. Cover with plastic film and refrigerate for at least 4 hours to allow the roulade to set.
Transfer the roulade to a serving platter (Once you have decorated the cake, it is difficult to move, so it is best to work directly on the presentation plate). Using a serrated knife, cut a 1½-inch thick slice from both ends of the roll. These will be used to form “gnarls” on the finished log.
Using an offset spatula, generously coat the entire log with all but about 1 cup of the buttercream, spreading from left to right in long streaks. Place the 2 reserved slices on top of the log, positioning one at each end and a little off center. Cover the slices with butter cream, using the offset spatula to smooth the top of each piece. Pull a cake comb through the buttercream on the cake so that it resembles tree bark. Then pull the comb up the sides of the slices so that they resemble gnarls on a tree. Place in refrigerator for about 15 minutes to allow the buttercream to set.
While the buttercream is setting, put the mushrooms together by gluing the caps to the stems with a dab of buttercream. Lay them cap side down until ready to place on the cake.
Remove the cake from the refrigerator. Using a sharp knife, carefully peel chocolate shavings off the chocolate block, letting them fall over and around the cake. Arrange the mushrooms around the cake. Serve immediately.