- Cake:
- 2 teaspoons butter
- 1/3 cup all-purpose flour, sifted
- 1/3 cup unsweetened cocoa powder
- 1/4 teaspoon fine salt
- 4 eggs, separated
- 3/4 cup confectioners' sugar, divided
- 1 teaspoon vanilla extract
- Whipped Cream Filling:
- 1 cup heavy whipping cream
- 3 tablespoons confectioners' sugar
- 1 tablespoon sour cream
- Chocolate Ganache:
- 1/2 cup heavy whipping cream
- 8 ounces dark chocolate chips
- Preheat oven to 350 degrees F (175 degrees C). Grease a 9×13-inch jelly roll pan with 1 teaspoon butter and line with parchment paper. Grease parchment paper with 1 teaspoon butter.
- Whisk flour, cocoa powder, and salt together in a small bowl.
- Combine egg yolks, 1/4 cup confectioners' sugar, and vanilla extract in a bowl; beat with an electric mixer on medium-high speed until pale yellow, 3 to 4 minutes.
- Clean the beaters of the electric mixer. Beat egg whites in a bowl on medium-high speed until foamy, 1 to 2 minutes. Gradually add 1/2 cup confectioners' sugar and beat until stiff peaks form, 2 to 3 minutes more.
- Fold egg yolk mixture gently into the egg whites. Fold flour mixture in gradually until batter is smooth.
- Pour batter into the prepared jelly roll pan and spread evenly with an offset spatula.
- Bake in the preheated oven until a toothpick inserted into the center comes out clean, 8 to 10 minutes. Let cool, about 30 minutes.
- Combine 1 cup heavy cream, 3 tablespoons confectioners' sugar, and sour cream in a bowl; blend with an electric mixer on medium-high speed until stiff, 1 to 2 minutes.
- Turn the jelly roll pan so the shorter side faces you. Spread whipped cream over the cake, leaving a 2-inch border at the top. Roll up cake toward the uncovered border, letting the parchment paper fall away as you roll. Place roll seam-side down on a serving platter.
- Place 1/2 cup heavy cream in a small saucepan over medium-low heat until warmed through, 3 to 5 minutes. Remove from heat and stir in chocolate chips. Let stand until chocolate softens, about 3 minutes. Stir with a spatula or wooden spoon until ganache is smooth and creamy.
- Drizzle chocolate ganache over rolled cake. Let stand until set, about 5 minutes. Run a fork through the ganache to create a tree bark effect.