Giant Mont Blanc

Preparation

1. Step 1

   Make the meringues: Set oven racks in the upper and lower thirds of the oven. Heat the oven to 225 degrees and line two large baking sheets with parchment paper. On one sheet of parchment, trace a 7-inch-wide circle and a 6-inch-wide circle. On the other sheet of parchment, trace a 4-inch-wide circle and a 2½-inch-wide circle. Flip the parchment papers upside down so the marks are underneath.

2. Step 2

   Place the egg whites in a large bowl, or in the bowl of a stand mixer fitted with the whisk attachment. Using an electric mixer, whisk the egg whites until frothy, 30 to 60 seconds. Add the cream of tartar if using, then, with the mixer on medium-high, gradually add the granulated sugar, 1 tablespoon at a time. Continue to beat until glossy and stiff peaks form, scraping down the bowl once or twice, 10 to 15 minutes. The meringue should not feel more than slightly gritty if rubbed in between your thumb and forefinger.

3. Step 3

   Spoon about 1 ½ cups/175 grams of meringue into the 7-inch circle and, using circular movements with the back of a large spoon, shape a 1-inch-deep divot in the middle. (This will be your Pavlova-style base, and should be big enough to hold about 1 ½ cups of filling later.) Use the remaining meringue to fill the smaller circles, spreading about ½ cup/70 grams into the 6-inch circle, ¼ cup/30 grams into the 4-inch circle, and about 2 tablespoons/10 to 15 grams into the 2½-inch circle. These three remaining meringues should be about ½ inch thick and fairly flat for neat stacking once baked. (You may have a small amount of meringue mixture left over.)

4. Step 4

   Bake meringues for 1½ hours, until crisp and dry to the touch. Turn off the oven and leave the meringues inside with the door slightly ajar (propping a wooden spoon in the oven door works well) until completely cool, at least 2 to 3 hours but overnight if possible.

5. Step 5

   Meanwhile, make the mocha crémeux: Combine the milk chocolate and salt in a small bowl and set alongside the stove, along with an empty medium heatproof bowl. Whisk together the egg yolks, cornstarch and instant coffee in a small heavy-bottomed saucepan until smooth. Gradually whisk in the milk. Take care to make sure it’s well combined, giving extra attention to the edges of the pan as you whisk.

6. Step 6

   Cook over medium heat, whisking continuously, until the mixture comes to a gentle boil and suddenly thickens to a pudding-like consistency, 2 to 3 minutes. Turn the heat down to low and whisk rapidly as the mixture gently simmers for 30 seconds longer. Immediately turn off the heat and whisk in the milk chocolate and salt until the chocolate is melted and the mixture is glossy. Immediately pour the crémeux into the heatproof bowl and cover with plastic wrap or parchment paper directly against the surface to prevent a skin from forming. Once cool to the touch, transfer to the fridge to chill completely and set, about 2 hours (and up to 3 days).

7. Step 7

   Make the chestnut topping: Combine the brown sugar, salt and ½ cup water in a small saucepan. Bring to a boil and cook for 1 minute, then turn off the heat and leave to cool for about 10 minutes.

8. Step 8

   When the sugar syrup has cooled, blitz the cooked chestnuts in the food processor for about 30 seconds, until finely ground, then slowly pour in the cooled sugar syrup while the motor is running. Blend until completely smooth, 1 to 2 minutes, scraping down the sides of the food processor bowl as necessary. Add the butter and blend until incorporated. The purée needs to be smooth and soft enough to pipe easily without breaking. If the chestnut mixture doesn’t seem smooth, pass it through a fine-mesh sieve. Set aside until ready to use. (The chestnut mixture can be made in advance and stored in the fridge for 5 days; bring to room temperature before using. After transferring it to the piping bag, you may need to rewarm it by kneading slightly with your hands until smooth.)

9. Step 9

   When you are ready to assemble, make the whipped cream: In a large bowl, whip the cream, mascarpone, powdered sugar and vanilla until very stiff peaks form, about 1 minute. This is the cement of your cake, so it needs to have enough body to provide structure in the layers.

10. Step 10

    To build, place the 7-inch meringue onto a serving plate. Using an offset spatula, spread a thin layer of whipped cream (½ cup/75 grams) across the base, pushing it up and over the sides of the meringue so it slightly overhangs the sides (you’ll fill in the hollow with the mocha crémeux shortly). You want a soft, cloudlike edge of cream that will peek out from under the chestnut strands when the Mont Blanc is assembled.

11. Step 11

    Give the mocha crémeux a quick stir, then dollop it into the hollow (it should fill it completely), smoothing it level with the cream.

12. Step 12

    Place the 6-inch meringue disk on top, pressing gently so it sits securely. Spread a thick layer of whipped cream (1¼ cups/150 grams) over the meringue and top with the 4-inch disk. Repeat with another generous layer of whipped cream (about half of what remains), then add the smallest disk. Finish with a final helping of the remaining whipped cream, shaping it into a conical peak with an offset spatula. Chill the Mont Blanc in the fridge for about 1 hour, until the cream has firmed up enough to support the chestnut strands you’ll add on top (be sure to give it a wide berth in the fridge).

13. Step 13

    When the Mont Blanc has finished chilling, transfer chestnut cream to a piping bag fitted with a 2-millimeter-wide round tip (the opening should be about the diameter of a strand of spaghetti) or a multihole tip. If you have a lazy Susan or rotating cake stand, place the mont blanc (still on its serving plate) on top of it — this will help with piping.

14. Step 14

    Starting from just above the overhang of cream at the base of the Mont Blanc, pipe the chestnut strands horizontally around the Mont Blanc, gradually working your way upward to cover the “mountain” completely with several layers of chestnut strands to create the look of a craggy mountain. (If using a lazy susan or rotating cake stand, gently rotate it as you pipe; if not, rotate the Mont Blanc 90 degrees as you cover each section.) Keep the pressure on the piping bag gentle and even, letting the strands fall naturally onto the cream rather than dragging the tip against it. Be sure to add several layers of strands, which will help create depth and fill in the gaps, creating the look of a craggy mountain. Don’t worry if a few strands break — they’ll blend in once the surface is covered. (You may not use all the chestnut puree.)

15. Step 15

    Store the Mont Blanc in the fridge until ready to serve: 2 to 4 hours is best, but up to 24 hours will work (though the meringue will be ever-softening!). Before serving (see Tip), garnish with candied chestnuts and a generous dusting of powdered sugar. To slice cleanly, wipe a large knife with a warm dishtowel and then wipe thoroughly dry between cuts.