Preheat the oven to 350°F. Line a 10x15-inch jelly roll pan with parchment paper, greasing the edges.
Beat egg yolks with 1/2 cup sugar until pale and fluffy. Mix in vanilla.
4 large eggs, 1 teaspoon vanilla extract
In another bowl, sift together flour, cocoa powder, and salt. Fold into the yolk mixture.
1/3 cup (47g) all-purpose flour, 1/3 cup (40g) natural unsweetened cocoa powder, 1/4 teaspoon salt
Beat egg whites until foamy, then gradually add the remaining 1/4 cup sugar. Beat to stiff peaks.
3/4 cup (150g) granulated sugar
Gently fold egg whites into the yolk mixture in thirds. Spread batter evenly in the prepared pan.
Bake for 10-12 minutes, until the cake springs back when lightly touched.
Dust a clean kitchen towel with powdered sugar. Turn the warm cake onto the towel and peel off parchment paper.
2 Tablespoons powdered sugar
Roll the cake tightly with the towel (starting from the short side) and let it cool completely.
Beat heavy cream, powdered sugar, and vanilla until stiff peaks form.
1 cup (240ml) heavy cream, 1/4 cup powdered sugar, 1 teaspoon vanilla extract
Heat cream in the microwave or on the stovetop until just steaming (do not boil). Pour over chopped chocolate and let sit for 2 minutes. Stir until smooth. Let cool slightly to thicken.
1 cup (240ml) heavy cream, 8 ounces (225g) dark chocolate
Unroll the cooled cake and spread the filling evenly over the surface. Roll it back up tightly (without the towel). Slice the roll approximately in half, then slice one of the halves on a diagonal and arrange the pieces to look like a log.
Place the roll seam-side down on a serving platter. Trim the ends for a clean look.
Spread ganache over the cake to resemble bark. Use a fork to create bark-like texture.
Arrange meringue mushrooms, sugared cranberries, and rosemary sprigs around and on the log for a festive look. Optionally, dust with powdered sugar for a snowy effect.
Chill for 1-2 hours before serving for easier slicing. Enjoy!