Tiramisu Mousse Cups

STEP 1: MAKE THE CREAM BASE (DAY BEFORE)

Heat the ½ cup (120 ml) heavy cream with the espresso powder until hot and the powder has dissolved. Pour over the white chocolate, let stand 1 minute, then stir until smooth. Cover with plastic wrap touching the surface and refrigerate for at least 4 hours, ideally overnight. It must be fully cold before whipping.

STEP 2: TEMPER THE CHOCOLATE

Melt two-thirds of the 300 g dark chocolate to 113–122°F (45–50°C). Off the heat, stir in the remaining third until melted and the chocolate cools to 88–90°F (31–32°C). Test a smear on parchment: it should set glossy and snap within 5 minutes at room temperature.

STEP 3: FORM THE CUPS

Spread six 2½-inch (6.5 cm) discs of tempered chocolate on parchment for the bases. Spread a thin, even layer of chocolate over each acetate strip. When it just loses its gloss, roll the strip into a tube inside the round cutter, chocolate side in, tape the seam and stand it on a base disc. Seal the joint with a little extra chocolate. Leave to set at cool room temperature for 30 minutes, then chill for 10 minutes. If the walls look thin, add a second coat once the first has set. Leave the acetate on until serving.

STEP 4: BAKE THE SPONGE BISCUIT DISCS

Heat the oven to 375°F (190°C) and line a baking sheet with parchment. Whisk the egg whites to soft peaks, then add half the sugar and whisk to firm, glossy peaks. In a separate bowl, whisk the yolks with the remaining sugar until pale and thick. Fold the yolks into the whites, then sift in the flour and cornstarch and fold gently. Pipe twelve 2-inch (5 cm) spiral discs with the plain tip, dust with powdered sugar and bake for 8–10 minutes until lightly golden and springy. Cool. The extra discs allow for breakage.

STEP 5: MAKE THE WALNUT PRALINE CRUMB

Melt the ¼ cup (50 g) sugar in a dry pan over medium heat to a deep amber caramel. Stir in the toasted walnuts, pour onto parchment and leave to harden. Blitz or crush to a fine crumb and store airtight.

STEP 6: MAKE THE MOUSSE

Melt the 150 g dark chocolate with the butter over barely simmering water, then cool to about 104°F (40°C). Whisk in the egg yolks one at a time, then the brandy and coffee liqueur. Whip the cream to soft peaks. In a clean bowl, whisk the egg whites with the salt to soft peaks, then add the sugar and whisk to glossy, medium peaks. Fold one-third of the cream into the chocolate to loosen it, then fold in the rest. Finish by folding in the meringue in two additions, stopping as soon as no streaks remain; overfolding knocks out the air and makes the mousse dense.

STEP 7: ASSEMBLE

Stir together the espresso, coffee liqueur and brandy for the soak. Dip each sponge disc briefly in the soak (moist, not dripping) and press one into the base of each cup. Pipe in the mousse with the plain tip until each cup is about two-thirds full, giving a deep mousse layer of around 1½ inches (4 cm). Tap gently to level. Chill for at least 4 hours, until set.

STEP 8: FINISH THE CREAM AND DECORATE

Whip the cold cream base with the mascarpone, powdered sugar and vanilla to firm, pipeable peaks; don't overwhip, or it will turn grainy. Pipe a crown of cream over the mousse with the star tip. Dust lightly with cocoa powder and scatter over a pinch of praline crumb. Peel off the acetate just before serving.