Bûche de Noël (Christmas Yule Log)

Instructions

1. Make meringue mushrooms up to 3 days ahead. Preheat the oven to 225º. Line the baking sheet with parchment and set aside.
2. Use an electric mixer to whip egg whites till foamy. Add cream of tartar, salt, and vanilla. Continue whipping till egg whites form soft peaks (if you make a peak with the meringue, the tip will not stay upright).
3. Slowly add the sugar while continuing to whip on high…a tablespoon or so at a time…till the whites form stiff peaks (the peaks will stay upright).
4. Place the meringue in a pastry bag fitted with a large plain tip. Or do what I do and use a ziplock bag fitted with a large plain tip. For stems, press out a bit of meringue onto the baking sheet and lift the tip straight up.
5. For caps, squeeze out round mounds of meringue. I just used a teaspoon dough scoop to form my rounds. You can use a wet finger to gently pat down any major imperfections.
6. Bake for 1 hour. Remove from oven and cool completely.
7. To make mushrooms, melt semi-sweet chocolate in the microwave…stopping and stirring at 30-second increments till melted. Add vegetable oil and stir. Use a toothpick to make a hole in the bottom of the cap…just large enough to insert one of the stems. Spread a small amount of chocolate on the underside of the cap and connect the stem to the cap.
8. It may take a bit of fiddling to make the holes the correct size and to get the mushrooms to stand alone. You should have plenty of caps and stems with which to practice. Dust mushrooms with cocoa powder to finish.
9. Make chocolate buttercream. Melt chocolates in the microwave, stopping and stirring at 30-second increments till smooth. Let cool slightly.
10. Beat the butter in a medium bowl until creamy. Add the chocolate, powdered sugar, cocoa powder, milk, and vanilla. Beat until it reaches a spreading consistency. Cover with plastic until ready to use.
11. To make the cake: Preheat oven to 350º. Butter 10½ x 15½ x 1-inch jelly roll pan. Line with parchment paper then butter and flour paper. Tap out excess flour.
12. Sift flour, cocoa, and baking soda twice into a medium bowl. Set aside while you clarify the butter. Over low heat, melt butter. Skim off the white foam and then pour the butter into a bowl, leaving any white solids that remain in the pan. Set aside and don’t forget to add this to the cake batter (I nearly did).
13. In a medium heat-proof bowl, whisk together sugar and eggs. Place over a pot of simmering water and heat and whisk till the mixture is warm and sugar is dissolved. Remove from heat and beat on high till tripled in volume, this will take about 5 minutes. Be patient. Reduce speed to medium and add vanilla. Beat another few minutes.
14. Sift about a third of the dry ingredients into the egg mixture. Fold in with a spatula. Repeat two more times, adding in the butter with the last addition.
15. Spread batter evenly in the prepared jelly roll pan. Bake for 15-20 minutes, till cake, pops back up when lightly tapped. Do not over-bake. Place on rack till cool enough to handle.
16. Dust the top of the cake with cocoa powder. Cut around the perimeter of the cake to loosen. Place a piece of waxed paper over the top of the cake, followed by a damp dishtowel.
17. Invert the cake onto a work surface, peel off the parchment, and sprinkle with cocoa. Starting with one short end, carefully roll up the cake in the towel. Wrap in plastic if desired and refrigerate till needed.
18. Make ganache: Microwave cream in a large measuring cup till hot. Add chocolate and whisk till smooth. Refrigerate till cold.
19. Whip cold ganache at medium speed till it has the consistency of soft butter. Start assembling the cake.
20. To assemble: Carefully unroll the cake onto the backside of a baking pan. Discard the wax paper and any plastic wrap.
21. Spread mousse on cake leaving a one-inch margin on each long edge.
22. Reroll cake starting with the other end…using a towel to help roll. Cover with plastic and chill for one hour.
23. Ice with the ganache. Make lines or ridges on the cake to resemble tree bark if desired. Garnish with meringue mushrooms.