Bûche de Noël

Instructions

1. Prepare the cake base
   Preheat oven to 350°F (175°C). Line a 10×15-inch jelly roll pan with parchment paper, leaving an overhang on all sides. In a large bowl, beat egg yolks with 100g sugar until pale and fluffy. Stir in vanilla extract.
2. Make the sponge batter
   In a separate bowl, whip egg whites until foamy. Gradually add remaining 50g sugar and continue beating until stiff peaks form. In another bowl, sift together flour, cocoa powder, and salt. Fold dry ingredients into yolk mixture. Gently fold in egg whites until just combined, being careful not to deflate the mixture.
3. Bake the cake
   Spread batter evenly into prepared pan. Bake for 12-15 minutes until cake springs back when touched. While still hot, dust with cocoa powder and cover with a clean kitchen towel. Place another baking sheet on top and carefully flip over. Peel off parchment paper and roll cake with towel from short end. Let cool completely, about 1 hour.
4. Prepare chocolate buttercream
   Melt chocolate in a heatproof bowl over simmering water; let cool slightly. In a stand mixer, beat butter until creamy. Gradually add confectioners' sugar, beating until fluffy. Add melted chocolate, heavy cream, and espresso powder if using. Beat until smooth and well combined.
5. Assemble the cake
   Carefully unroll cooled cake and remove towel. Spread about 1/3 of the buttercream evenly over the cake, leaving a 1-inch border. Re-roll cake (without the towel) and place seam-side down on a serving platter. Cut off a small diagonal piece from one end and attach it to the side of the log to create a branch.
6. Decorate the log
   Cover the entire cake with remaining buttercream, using a fork to create bark-like textures. Don't smooth it perfectly - the rough texture makes it look like tree bark. Refrigerate for at least 1 hour to set.
7. Final decoration
   Just before serving, arrange rosemary sprigs to look like pine needles. Add meringue mushrooms if using. Dust lightly with powdered sugar to resemble snow. For an extra touch, you can add cranberries or small holly leaves (not to be eaten) for a festive appearance.