Heat oven to 350. Butter a 9×13 jelly roll pan and line with parchment; butter the parchment. I used a silicone mat.

Whisk together the flour, cocoa, and salt in a small bowl.

Beat the egg yolks, vanilla, and 1/4 cup of the sugar in a medium bowl with an electric mixer on medium-high until light yellow, 3-4 minutes.

In a separate bowl, beat the egg whites (with clean beaters) on medium-high until foamy, 1-2 minutes. Gradually add 1/2 cup of the remaining sugar and beat until stiff peaks form, 2-3 minutes or more.

Gently fold the egg yolk mixture into the egg whites. Gradually fold in the dry ingredients. Transfer the mixture to the prepared pan and use an offset spatula to smooth the surface. Bake until the cake springs back lightly when pressed, 8-10 minutes (mine actually took about 12 minutes). Cool.

Whip the heavy cream, sour cream, and the remaining 3 tablespoons of sugar in a medium bowl with an electric mixer on medium-high until stiff peaks form, 1-2 minutes.

Spread the whipped cream on the cake, leaving a 2-inch border along one of the short ends. Starting at the other short end, roll up the cake toward the uncovered border (letting the parchment fall away as you roll…I actually took off the silicone mat before this moment). Place the cake seam-side down on a serving platter. Drizzle with chocolate ganache over the top (recipe to follow). Let set for 5 minutes. Run the tines of a fork through the ganache to create “bark.” (“Buche de Noel” is French for “Yule log”).

Make the chocolate ganache by bringing 1/3 cup heavy cream to a boil in a small pot. Do not over-cook. Remove from heat, add the chocolate, and let stand for 5 minutes. Whisk to combine. Cool slightly before using.

Optional: For toppings of candied rosemary and candied raspberries, I followed this tutorial. Candied cranberries would be another beautiful addition.