Buche de Noel (yule log)

https://smittenkitchen.com/2011/04/heavenly-chocolate-cake-roll/

Also useful as a Passover flour-free cake!

Cake:
1 cup semi- or bittersweet chocolate chips
3 tablespoons water 
6 large eggs, at room temperature, separated
2/3 cup sugar
1/4 teaspoon table salt

2 tablespoons unsweetened cocoa powder, divided (to sift on at the end)

Filling:
1 cup heavy or whipping cream
2 to 3 tablespoons powdered sugar (use more if you prefer a sweeter filling)
1/2 teaspoon vanilla extract or 1 to 2 tablespoons liqueur of your choice, such as Grand Marnier

1. Preheat oven to 350°F. Butter or oil a 10-by-15-inch shallow baking or jellyroll pan. Line the bottom lengthwise with a piece of waxed or parchment paper that extends up the short sides one inch.

2. Melt chocolate with the 3 tbsp water in microwave on low heat, taking out to stir until just smooth

3. In a clean bowl beat egg whites until stiff, set aside

4. Beat egg yolks with an electric mixer until pale and creamy. Add sugar gradually, and continue to beat until yolks are pale and ribbony. Gently stir the semi-cooled chocolate into the yolk mixture.

5. Stir 1/4 of egg white mixture into the chocolate-yolk mixture to lighten it. 

6. Fold the remaining whites into the cake batter in three additions. Pour batter into prepared pan and smooth top. Bake in preheated oven for 15 minutes, or until cake layer feels dry (but very soft) to the touch and a toothpick inserted into the center comes out clean. It will still seem a little underbaked.

7. Transfer to a cooling rack and cover the top with a light damp towel or two layers of damp paper towels for 10 minutes. Gently remove towels; don’t fuss if they have a bit of cake stuck to them. Run a knife around the edges of the cake. 

8. Sift one tablespoon cocoa over the top of the cake and cover the cake with a thin tea or flour sack towel [Updated, see Note above] that is a little longer than the pan. Place the back of a baking sheet or a large flat tray over the towel and invert the cake and paper onto it. Gently peel back the parchment or waxed paper that lined the pan. Sift the remaining tablespoon of cocoa powder over the top of the cake (that was, one minute ago, the underside). Using the towel underneath to help lift and roll the cake, roll the cake from short end to short end with the towel inside. Let cool completely, encased in its towel.

9. Once cool, beat heavy cream with powdered sugar and vanilla until it holds stiff peaks. Get your serving plate ready and place it near your cake roll. Gently unroll chocolate cake and remove tea towel. [Try to get the tea towel to the hamper without touching anything, as it is saturated with smudgy cocoa and trust me, can mess up a white kitchen fast.] Spread whipped cream filling evenly over cake. Gently use waxed or parchment paper once again to reroll cake. Place on serving platter, seam side down.

Frost with Magnolia buttercream frosting: https://keekitchen.blogspot.com/2012/09/magnolias-chocolate-buttercream-frosting.html