Preheat the oven to 350°. Butter two 12-by-17-inch rimmed baking sheets and line them with parchment paper, leaving a 1-inch overhang on all of the short sides. Butter the paper and dust with flour.

In a small bowl, whisk the 1 cup of flour with the cocoa and salt. In another small bowl, combine the chocolate and espresso. In the bowl of a standing electric mixer, combine the egg yolks with 2/3 cup of the sugar. Set the bowl over a pan of simmering water and whisk until the sugar is dissolved. Transfer the bowl to the mixer fitted with the whisk and beat at high speed until the yolks are pale and thick, about 5 minutes. Beat in the melted chocolate mixture along with the vanilla. Transfer to a large bowl.

Thoroughly wash and dry the mixer bowl and the whisk. Beat the egg whites with the cream of tartar on moderately high speed until soft peaks form. Gradually add the remaining 2/3 cup of sugar and continue beating at high speed until the whites are glossy, about 2 minutes longer. Whisk one-fourth of the egg whites into the cake batter, then fold in the remaining whites until no streaks remain.

In a small bowl, whisk the melted butter with 1/2 cup of the batter; fold this mixture into the batter. Working in 2 batches, sift the cocoa powder mixture over the batter and gently fold it in. Divide the batter between the prepared pans, spreading it out to fill the pans. Bake for about 18 minutes, until the cake feels springy and dry; shift the pans from top to bottom and front to back halfway through baking. Transfer the pans to racks to cool completely. Run the tip of a knife around the edges, cover with parchment paper and a baking sheet and invert; peel off the parchment on top.

Spread the Malted Buttercream over the cakes. Using a ruler, cut each cake precisely in half lengthwise, cutting through the paper; you should have four 6-by-17-inch strips of cake. Roll one strip into a tight coil, leaving the paper behind. Roll the 3 remaining cake strips around the coil in the same way to form a very wide, short jelly roll. Set the cake on a large plate, spiraled end up. Frost the outside of the cake with the Dark Chocolate Buttercream. Refrigerate until set, at least 8 hours. Decorate the cake with meringue mushrooms, cranberries and rosemary sprigs and serve, cutting the cake into wedges or horizontal slices.

FOR THE DARK CHOCOLATE AND MALTED BUTTERCREAMS

5 large egg whites, at room temperature

1 1/2 cups sugar

1 teaspoon pure vanilla extract

2 cups (4 sticks) unsalted butter, at room temperature

4 ounces good-quality dark chocolate (60-72%), melted and cooled

1/4 cup malt powder

12 malted milk balls candies, crushed

MAKE THE DARK CHOCOLATE AND MALTED BUTTERCREAMS

In the bowl of a standing electric mixer, combine the egg whites and sugar. Set the bowl over a pot of simmering water and whisk until the sugar is dissolved and the egg whites are just warm to the touch. Return the bowl to the mixer and fit it with the whisk attachment. Add the vanilla and beat the egg whites at high speed until firm and glossy, about 5 minutes. With the machine running, whisk in the butter a few tablespoons at a time. If the mixture begins to look curdled, continue to beat until smooth before adding more butter.

Transfer 1 1/2 cups of the buttercream to a bowl and whisk in the melted chocolate. Cover the chocolate buttercream and refrigerate.

Dissolve the malt powder in 2 tablespoons hot water, then beat it into the buttercream remaining in the mixer. Beat in the crushed milk balls. Cover the malt buttercream and refrigerate.

Meringue Mushrooms

Baked Explorations by Matt Lewis and Renato Poliafito, pages 194-195

3 large egg whites, at room temperature

¾ cup sugar

¼ teaspoon cream of tartar

1 ounce good-quality white chocolate, melted and cooled (I actually used semisweet)

2 ounces dark unsweetened cocoa powder, (like Valrhona) for sifting over assembled mushrooms

Preheat the oven to 200 degrees F. Line two sheet pans with parchment paper.

Whisk the egg whites and sugar together in the heat proof bowl of a standing mixer. Set the bowl over a saucepan of simmering water (double boiler method). Cook, whisking constantly, until the sugar is completely dissolved and the mixture registers 140 degrees F on an instant-read thermometer, 6 to 8 minutes.

Transfer the bowl to a standing mixer fitted with the whisk attachment. Beat it on high speed until stiff peaks form. Add the cream of tartar when the mixture begins to thicken, or after 3 minutes. Keep beating for another minute or so until stiff peaks hold.

Fill a pastry bag fitted with a large round tip with the meringue. To make the caps, hold the pastry bag close to the parchment paper-lined pan and pipe out a small dome (about a tablespoon) of meringue, pulling up at the very end  of piping to give your cap some height.

To form mushrooms stems, hold the bag close to the parchment paper and pipe the meringue, pulling up as you go, into small cone shapes. Make the same number of stems as caps.

Place the pans in the oven and bake the meringue pieces for 90 minutes, rotating the baking sheets halfway thought the baking time. Turn off the oven, prop the door slightly open and leave the meringues in place for at least 2 hours longer, or overnight.

ASSEMBLE THE MERINGUE MUSHROOMS

Turn the caps over and use a toothpick to make a tiny hole large enough to fit the tip of the stem into. Fill the hole with a tiny bit of white chocolate (or semi sweet-which is what I used). Gently press the stem into place and allow the chocolate to set. Sift cocoa powder over the assembled mushrooms.

Sugared cranberries and sugared rosemary

¼ cup superfine sugar

1 cup granulated sugar

1 cinnamon stick

¾ cup fresh cranberries

10 rosemary sprigs

Line a half-sheet pan with parchment paper. Place the superfine sugar in a small bowl.

In a medium saucepan, stir together 1 cup of water with the sugar, then add the cinnamon stick. Bring the mixture to a boil over medium-high heat and stir until the sugar is completely dissolved. Remove from the heat and pour into a heatproof, wide-mouthed bowl. Let the liquid cool for a few minutes, then remove the cinnamon stick.

Drop the cranberries in the syrup and stir to coat the cranberries completely. Remove the cranberries, a few at a time, with a slotted spoon (tap the spoon to release excess syrup) and drop them in the superfine sugar. Toss the cranberries in the sugar to coat completely, and place on the parchment paper to dry. Repeat the above procedure with the rosemary. Decorate the stump as you wish.