Buche de Noel

Chocolate Genoise Cake:

• Heat oven to 400 degrees. Line a 12-by-17-inch jellyroll pan with parchment paper, and set aside. In the bowl of an electric mixer fitted with the whisk attachment, beat egg yolks on high speed until pale yellow, 4 to 5 minutes. Transfer to a medium bowl, and set aside. Wash and dry the whisk attachment and mixer bowl.
• Place egg whites in bowl of electric mixer fitted with the whisk attachment. Beat on medium speed until soft peaks form, 1 to 2 minutes. Increase speed to medium high, and add sugar gradually, whipping until stiff peaks form. Transfer egg-white mixture to a large bowl.
• Using a rubber spatula, fold egg-yolk mixture into egg-white mixture. Sift cocoa powder and flour over top, and gently fold in. Pour batter into prepared pan, and smooth top with an offset spatula.
• Bake until cake springs back when touched, 9 to 10 minutes. Remove pan from oven, and immediately turn cake out onto a wire rack lined with parchment paper. Peel parchment paper from top of cake, and cool completely.
• Place a clean kitchen towel on work surface. Transfer cake on parchment paper to towel. Using an offset spatula, spread white-chocolate mousse over cake.
• With a short end of cake facing you, roll carefully into a roulade. Wrap in a kitchen towel, and secure with clothespins or large metal binder clips to hold the roll in a tight round shape. Place on a baking sheet, and refrigerate until firm, at least 2 hours.
• Remove from refrigerator, and unwrap. Using a serrated knife, trim the ends of the roll, cutting on the bias. Choose the more presentable end, and place it, cut-side up, on the log, forming a branch. If desired, use the other cut end for a second branch.
• Transfer the log to a serving platter. Slide 5-inch strips of parchment paper under the log to protect the tray while decorating. Coat with seven minute frosting using an offset spatula. Remove parchment pieces. Decorate with meringue mushrooms, powdered sugar and cocoa, and whatever else strikes your holiday fancy.
• Makes one 10-by-5-inch log.

White Chocolate Mousse: (filling for the buche de noel)

• Dissolve gelatin in 1/4 cup cold water, and set aside for 5 minutes. Place chocolate in the bowl of a food processor, and pulse until very finely chopped.
• Prepare an ice-water bath; set aside. Place 3/4 cup cream in a small saucepan, and bring just to a boil over medium-high heat. Add gelatin, and stir for 30 seconds to dissolve completely. Pour into food processor with the motor running, and process until chocolate mixture is smooth.
• Transfer to a medium bowl and place over ice water bath. Chill until mixture is thick enough to fall from a spoon in ribbons.
• Whip remaining 1 3/4 cups heavy cream to soft peaks. Fold into chocolate mixture. If not using immediately, refrigerate in an airtight container.
• Makes 5 1/2 cups.

Coffee Buttercream: (frosting for the buche de noel)

• Whisk the egg whites and sugar together in the bowl of an electric mixer. Set the bowl over simmering water and whisk gently until the sugar is dissolved and the egg whites are hot. Attach the bowl to the mixer and whip with the whisk on medium speed until cooled. Switch to the paddle and beat in the softened butter and continue beating until the buttercream is smooth. Dissolve the instant coffee in the liquor and beat into the buttercream. Reserve to be used as frosting for the yule log.

for swiss meringue:

• Fill a medium saucepan one-quarter full with water. Set over medium heat; bring water to a simmer.
• In the bowl of an electric mixer, combine egg whites, sugar, and cream of tartar; place over saucepan. Whisk constantly until sugar is dissolved and whites are warm to the touch, about 3 minutes. Rub mixture between fingers to test.
• Transfer bowl to mixer stand, and whip, starting on low speed and gradually increasing to high, until meringue is cool and stiff, glossy peaks form, about 10 minutes. Add vanilla; mix until combined. Use immediately. (Makes 4 cups)

for the meringue mushrooms:

• Heat oven to 200 degrees. Place Swiss meringue in an 18-inch pastry bag fitted with a large 3/4-inch round tip. Line two baking sheets with parchment paper. Pipe meringue, forming domes 1 to 2 inches in diameter. Pipe a stem shape for each dome by piping what looks like a stretched hershey's kiss. Bake for 1 hour; reduce heat to 175 degrees, and continue baking until meringues are completely dry to the touch but not browned, 45 to 60 minutes more.
• Poke a small hole in the center of each mushroom cap using a paring knife or a small pastry tip. Dip the pointed end of each of the mushroom stems in reserved swiss meringue, and insert into hole in center of cap. Allow to set. Meringue mushrooms should be kept in an airtight container in a cool, dry place. (Makes about 20)