Classic Chocolate Yule Log

Ingredients

• For the cake:
• 2 1/2 ounces pistachio oil, roasted hazelnut oil, or melted butter
• 2 1/2 ounces finely chopped dark chocolate, between 85% and 100%
• 1/2 ounce vanilla extract
• 5 large eggs
• 5 3/4 ounces sugar
• 1 tablespoon instant espresso powder
• 3/4 teaspoon baking powder
• 1/2 teaspoon Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 1/2 teaspoon baking soda
• 1 1/4 ounces water
• 3 3/4 ounces bread flour
• For the ganache frosting:
• 12 ounces finely chopped dark chocolate, between 55% and 75%, or a blend thereof
• 12 ounces heavy cream
• Salt and vanilla to taste
• For the filling:
• 2 cups sweetened whipped cream, buttercream, or other frosting, see note, weight will vary
• To Garnish:
• Matcha powder, optional
• Cocoa powder, optional
• 1 recipe meringue mushrooms, optional

Directions

1. Set a rack in the lower-middle of the oven and heat it to 350 degrees F. Line the bottom of an aluminum half-sheet pan with parchment, then coat the pan with oil or pan spray.
2. For the cake, warm the butter, or the oil, in a 1-quart stainless steel saucier over medium-low heat until very hot, about 200 degrees F. Take the pan off the heat, add the chopped chocolate and vanilla, and whisk until the mixture is smooth. Hold it aside only while you continue with the next steps, because it will firm up as it sits and become difficult to blend into the batter. You want this chocolate mixture loose and warm when it goes in, around 100 degrees F, though there is no need to take its temperature as long as it is still pourable.
3. In the bowl of a stand mixer with the whisk attachment, add the eggs, sugar, instant espresso, baking powder, salt, and baking soda. Beat on medium-low until the sugar is dissolved and the dark brown mixture looks smooth, even, and liquid, with bubbles starting to show throughout, about 3 minutes.
4. Turn the mixer up to medium and whip until the mixture becomes dark tan and noticeably lighter and fuller than it was. It should still flow, but it will be thick enough to stream from the whisk in narrow ribbons, about 5 minutes. Raise the speed to high and keep whipping until the eggs are thick and foamy, pale brown, and about doubled, with a clear vortex showing as the mixer runs, about 8 minutes. When the mixture falls from the whisk back into the bowl, it should briefly pile on itself before smoothing out. The timing is only a guide, since stand mixers vary, so trust the texture and appearance most.
5. When the egg foam is thick and fluffy, lower the speed to medium-high and add the water right away, then pour in the warm chocolate mixture. Drop the speed to medium-low and add the sifted flour. Once the flour is almost blended in, stop the mixer and take off the whisk attachment. Holding the top of the attachment, use the whisk by hand to give the batter a few final strokes and finish working in the flour. Use a flexible spatula to fold the batter up from the bottom once or twice, then scrape it into the prepared pan and smooth it evenly with an offset spatula. Bake until the cake has risen well and feels set, but is still soft and puffy enough to hold a slight mark when gently pressed, about 12 minutes. Do not let it go too far, or it will be more likely to crack when rolled.
6. As soon as the cake comes out of the oven, cover the half-sheet pan with 2 large strips of foil. Using a kitchen towel or oven mitt, crimp the foil snugly around the rim of the pan. Leave the cake to cool to about 70 degrees F/21 degrees C. This is just a reference point, and touch is fine here: if the cake is warm, it can melt the filling, but if it is cold, it can split as you roll it.
7. For the ganache, while the cake cools, heat the cream in a 2-quart stainless steel saucier until it reaches a simmer. When bubbles appear, take it off the heat. Whisk in the chocolate, then season to taste with salt and vanilla, or any other extracts and flavorings you want. Let the ganache stand until it cools and thickens to a spreadable, frosting-like texture, about 2 hours, or around 75 degrees F.
8. To assemble the Yule log, run a butter knife around the edges of the cooled cake to release it from the pan. Spread about 2 cups of freshly whipped cream, plain or flavored, buttercream, frosting, or jam evenly over the cake. Starting at the widest side, lift the cake with the parchment and carefully fold the edge inward so it rolls over itself. Keep rolling with the parchment to help lift and guide the cake; the paper will pull away naturally as you go.
9. If desired, cut a 4-inch piece from the cake on a sharp angle to make a branch. Transfer the cake to a large platter, then set the branch against the main roll so it fits snugly. You can also stand the branch upright, securing it with a few drinking straws pushed through the branch and into the log. Once the pieces are positioned however you like, cover the roulade with a thick coating of ganache.
10. When the ganache starts to firm up, pull the tines of a fork along the length of the cake and over the branches to make a bark-like texture. Go over any areas again as needed to rough up the surface. Finish with matcha for moss, cocoa for dirt, and meringue mushrooms, if using. Serve right away, or wrap tightly in plastic until you need it. Cakes with whipped cream filling can be refrigerated up to 36 hours and are best after sitting at room temperature for a few hours before serving. Cakes with buttercream or frosting filling can be kept at cool room temperature for up to 36 hours.