Kumquat and Chocolate Yule Log

Preparation

1. Step 1

   Prepare the marmalade: Trim and discard the ends of the kumquats, slice the kumquats into ⅛-inch/¼-centimeter rounds and discard the seeds (pips). If using tangerines, quarter them lengthwise then cut them into ⅛-inch/¼-centimeter-thick slices. Transfer the fruit, star anise, cinnamon, vanilla and 2 cups/450 milliliters water to a large saucepan. Bring to a boil over medium-high heat and cook until the fruit has softened, about 10 minutes.

2. Step 2

   Add the sugar and lemon juice and cook, stirring often, until the marmalade darkens and has a loose, jam-like consistency, adjusting the temperature as necessary to maintain a rapid bubble, 15 to 25 minutes, depending on the juiciness of your fruit. (You don’t want to overcook the marmalade, as it will continue to thicken as it cools.)

3. Step 3

   Remove from the heat and stir in the orange juice and Cognac. Let cool at least 1 hour. Discard the star anise and cinnamon sticks.

4. Step 4

   Prepare the cake: Heat oven to 350 degrees Fahrenheit/170 degrees Celsius. Grease the base and sides of a 9-by-13-inch/23-by-33-centimeter jellyroll pan (Swiss roll tin) with butter. Line the base with parchment paper, grease the paper and set aside.

5. Step 5

   Melt 2½ tablespoons/35 grams butter and 1 ounce/35 grams chocolate in a large heatproof bowl set over a medium saucepan of simmering water over medium-low heat, stirring frequently, until melted, 2 to 3 minutes, then set aside to cool. Sift the flour, coffee powder, salt, baking powder, baking soda (bicarbonate of soda) and ¼ cup/20 grams cocoa powder into a medium bowl and set aside.

6. Step 6

   Place the eggs, yolks, brown sugar and zest in the bowl of a stand mixer. Using the whisk attachment, whisk the mixture on high speed until thick, pale and tripled in volume, about 2 minutes. Reduce the speed to medium-low, add the melted chocolate mixture, and mix until combined, about 30 seconds.

7. Step 7

   Using a spatula, gently fold in the flour mixture. Pour the mixture into the prepared pan (tin) and smooth it into an even layer. Bake until the cake has just set and springs back slightly to the touch, 6 to 8 minutes. (The cake will continue to cook as it cools, so resist the urge to overbake.) Let cool for 5 minutes.

8. Step 8

   Sift 1½ teaspoons cocoa powder over the top of the cake, then cover with a clean tea towel. Place a wire rack on top of the towel and quickly flip the cake over, removing the pan and paper. Sift the remaining 1½ teaspoons cocoa powder over the top of the cake. With one of the shorter ends facing you, roll the still-warm cake lengthwise into a roulade, with the towel inside, and let cool completely.

9. Step 9

   Prepare the caramel shards: Line a small baking sheet (tray) with parchment paper. Add the sugar and 1 tablespoon water to a small saucepan. Cook over medium-high heat, gently swirling the pan until the sugar melts and the caramel turns a medium amber color, about 5 minutes. Immediately pour the caramel onto the prepared sheet and spread it out as thinly as possible using an offset spatula. Let cool until firm.

10. Step 10

    Prepare the date-and-orange cream: Add the dates, orange zest and juice, Cognac and star anise to the bowl of a stand mixer. Using the paddle attachment, mix on medium-low speed until the dates are roughly crushed, about 30 seconds. Add the cream and mascarpone, increase the speed to medium-high and continue mixing until soft peaks form, 1 to 2 minutes. (You can make the cream 1 day in advance and keep it refrigerated.)

11. Step 11

    Prepare the meringue topping: If necessary, reheat the oven to 350 degrees Fahrenheit/170 degrees Celsius. Add the sugar to a small baking pan (roasting tin) lined with parchment paper and warm in the oven, 8 minutes. Meanwhile, place the egg whites in the bowl of a stand mixer. When the sugar is 1 minute away from being done, using the whisk attachment, whisk the eggs whites on medium-high speed until frothy.

12. Step 12

    Turn the mixer off and carefully add the hot sugar, using the parchment paper as a funnel (chute). Increase the speed to high and whisk the meringue until stiff peaks form and the mixture is no longer grainy, about 3 minutes, scraping down the sides of the mixing bowl as necessary. Spoon ½ cup/70 grams into a piping bag and set aside.

13. Step 13

    Assemble the roulade: Gently unroll the cake but keep it on the tea towel. Using an offset spatula (or a regular spatula if you don’t have one), spread the date-and-orange cream evenly over the top of the cake, leaving a 1-inch/2-centimeter border at the short end farthest away from you. Distribute ½ cup/125 grams marmalade over the top of the cream by small spoonfuls and gently spread it out using the back of the spoon.

14. Step 14

    Starting with the short end closest to you, carefully roll the sponge into a roulade, using the cloth to help you. Dust the top of the cake lightly with confectioners' sugar and carefully transfer the roulade, seam side down, to a serving plate.

15. Step 15

    Melt the remaining 35 grams/1 ounce chocolate over a double boiler set over low heat, then drizzle the roulade with the melted chocolate and leave to set slightly, about 5 minutes.

16. Step 16

    Snip the end off the piping bag and pipe 1-inch-/3-centimeter-tall decorative spikes along the top of the roulade. (Pipe the remaining meringue mixture into small kisses and bake separately, if you wish.) Use a blowtorch to burn the meringue so it is scorched in spots. At this point you can refrigerate the roulade for a few hours, until ready to serve.

17. Step 17

    To serve, break the caramel into 2-inch/5-centimeter shards and stick them haphazardly into the meringue topping. Using a small fork, pick out pieces of citrus from the remaining marmalade and distribute them in between the shards. Use the chocolate shavings to fill any gaps in your decorations and serve.