Mont Blanc Cake

Instructions

1. In the bowl of a stand mixer fitted with the whisk attachment, combine the room-temperature egg whites and cream of tartar. Begin beating on medium speed until foamy. Gradually add one-third of the granulated sugar while continuing to beat. While the mixer is running, prepare your workspace: line two baking trays with parchment paper (greased on both sides for easy release) and fit a pastry bag with a large round piping tip.Once the sugar is incorporated, increase the mixer speed to high. Gradually add the remaining granulated sugar and continue beating until the meringue reaches stiff, glossy peaks. Stop the mixer. Gently fold in the lime zest and sifted powdered sugar by hand until just combined.Immediately pipe the meringue onto the prepared trays, forming narrow peaks no larger than 1.5" (4 cm) wide and 2" (5 cm) tall.

2. Meringues must be dried at a very low temperature. Higher heat will cause them to crack and brown prematurely. Preheat the oven to 212°F (100°C). Bake the meringues for 1 hour or longer. Turn the oven off and leave the meringues inside with the door closed for an additional 30-45 minutes to finish drying gently. Remove the trays and allow the meringues to cool completely at room temperature.Store the completely cooled meringues in an airtight container (such as a metal tin or a freezer bag) in a cool, dry place. Do not refrigerate or freeze, as moisture will cause them to soften.

3. If they soften: If the meringues soften over time, you can briefly re-crisp them in a low oven (200°F / 95°C) for 5-10 minutes.For use in cakes: To prevent softening when layered in a cake, lightly coat each meringue with a thin film of tempered cocoa butter or refined coconut oil before assembly. This creates a moisture barrier.

4. Soak the gelatin sheets in a bowl of cold water until pliable, about 10 minutes. Drain and squeeze out any excess water. In a saucepan, combine the blackcurrant purée, water, and half of the sugar. Heat the mixture over medium heat until it just begins to simmer.In a separate small bowl, whisk the remaining sugar with the pectin to prevent clumping. Once the purée mixture is hot, gradually whisk in the sugar-pectin mixture. Bring the mixture to a full boil and cook, stirring constantly, for exactly 3 minutes to activate the pectin. Remove the saucepan from the heat. Immediately whisk in the lemon juice and the softened gelatin until the gelatin is completely dissolved.Carefully pour the hot gelée into half-sphere silicone molds. Tap the molds gently on the counter to release any air bubbles. Freeze overnight, or until completely solid. De-mold the frozen gelée spheres as needed. For best texture, allow them to thaw slightly in the refrigerator for 15-20 minutes before serving.

5. Soak the gelatin sheets in a bowl of cold water until completely soft and pliable, about 10 minutes. Drain, squeeze out excess water, and set aside.In a saucepan, combine the heavy cream (200g) with the lime zest. Heat over medium heat until it just begins to simmer. Pour the hot cream over the melted white chocolate. Using an immersion blender, blend from the bottom up. While the mixture is still warm, add the softened gelatin and blend again until it is fully dissolved. Add the remaining cold heavy cream and blend until the mixture is homogeneous and smooth. Refrigerate the base for at least 8 hours, or preferably overnight, to mature and fully set before whipping.

6. Prepare thin tartlet shells, blind bake them at 330°F (160°C) for 15 minutes, and let them cool.

7. In a food processor, combine the softened butter, almond flour, and powdered sugar. Process until the mixture is smooth and homogenous. With the processor running, add the room-temperature egg. Add the rum and mix just until combined. Scrape down the sides of the bowl as needed. Fill each pre-baked tartlet shell with approximately 1 ounce (30g) of almond cream, filling it to about 60% of the shell's capacity.

8. Bake at 330ºF/160ºC for about 25 minutes until golden brown. Let cool and set aside. Chestnut paste (pâte de marron) is an essential ingredient used by many professionals. It is indeed often mixed with chestnut cream (crème de marrons).

9. Mix all ingredients together.