Chocolate-Espresso Matzo Icebox Cake With Hazelnut Praline Whipped Cream

Instructions

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1. 1 For the Chocolate Mousse: In a large heatproof mixing bowl, combine chocolate and heavy cream. Set bowl over a saucepan filled with 1 inch of barely simmering water over low heat. Heat, stirring occasionally, until chocolate is fully melted, about 8 minutes. Remove from heat, then whisk in espresso powder and salt until smooth. Set on a heatproof work surface; let cool slightly, about 10 minutes. Once chocolate mixture is warm to the touch, whisk in egg yolks until well combined.
2. 2 Meanwhile, beat egg whites with a stand mixer fitted with the whisk attachment on medium speed until egg whites begin to foam. Slowly and steadily stream in sugar. Continue beating until mixture is glossy and reaches medium-stiff peaks, 4 to 6 minutes. ​​Alternatively, combine cream, sugar, and salt in a large mixing bowl. Using a hand mixer and beat on medium speed until medium medium peaks form, 3 to 5 minutes.)
3. 3 Add 1/4 of the meringue to the cooled chocolate mixture and gently fold until thoroughly combined. Add remaining meringue and continue to gently fold until meringue is almost entirely incorporated, being careful not to overmix.
4. 4 Line a 9- by 4-inch loaf pan with plastic wrap. Pour hot espresso in an 8-inch square pan or other large shallow dish. Using a flexible spatula or offset spatula, spread about 1 cup of chocolate mousse on the bottom of prepared loaf pan. Soak 1 sheet of matzo in espresso until softened but not disintegrating, about 30 seconds per side. Cover mousse with 1 layer of the soaked matzo (break or cut the sheet so it fits snugly in an even layer). Gently press into mousse. Repeat soaking matzo and layering with mousse 4 times, ending with mousse layer on top.
5. 5 Cover tightly with plastic wrap and refrigerate until cake is cohesive and chilled, at least 6 hours and up to 24 hours.
6. 6 For the Hazelnut Praline Whipped Cream: While cake chills, adjust oven rack to middle position and preheat oven to 325°F (165°C). On a large rimmed baking sheet, spread hazelnuts in an even layer. Bake until fragrant and toasted, 10 to 12 minutes. Transfer hazelnuts to a clean kitchen towel. Fold kitchen towel over, and rub hazelnuts between the towel to remove loose skins. Line a rimmed baking sheet with parchment paper and place nuts in a single layer in the center, discarding loosened skins.
7. 7 In a medium skillet, heat sugar over medium heat, undisturbed, until sugar begins to melt around the edges of the skillet. Continue cooking, stirring or swirling the skillet occasionally, until sugar reaches a medium amber color, about 8 minutes. Immediately pour hot melted sugar over hazelnuts on prepared baking sheet and set aside to cool completely and harden, about 30 minutes.
8. 8 Transfer 3/4 of the cooled candied hazelnuts to a food processor (reserve remaining nuts for garnish). Process until a smooth, peanut butter-like paste forms, stopping to scrape the sides as needed, about 5 minutes. Transfer to an airtight container and store at room temperature until ready to use or up to 1 week.
9. 9 Line a rimmed baking sheet with foil. Remove plastic from top of chilled cake and invert cake onto prepared sheet. Gently peel away remaining plastic, smooth sides with an offset spatula, and transfer to freezer until firm enough to slice, about 1 hour or up to 1 week.
10. 10 In a stand mixer fitted with the whisk attachment, whip cream and powdered sugar until soft peaks form, 2 to 3 minutes. Add 1/2 cup of the hazelnut praline paste (reserve any remaining paste for another use) and continue beating until just incorporated, about 5 to 10 seconds. Do not overbeat; if praline paste is not yet fully incorporated, continue folding by hand.
11. 11 Remove cake from freezer. Wiggle a chef's knife or long offset spatula under the cake to loosen it from the foil; transfer cake to a serving platter.
12. 12 Dollop hazelnut praline whipped cream over top of cake. Chop remaining reserved candied hazelnuts and sprinkle over top. Garnish with chocolate curls, if using.
13. 13 Using a hot knife, slice cake into 8 pieces and serve. (For cleaner cuts, run knife under warm water and dry knife with a clean kitchen towel before portioning each slice.)