Step 1: Prepare the Raspberry Sauce

1. Start by making the raspberry sauce. In a small saucepan, combine the raspberries, sugar, and lemon juice. Place the saucepan over medium heat and bring to a boil. Stir occasionally to help the raspberries break down and release their juices.
2. Once the mixture has boiled for about 10 minutes and slightly thickened, remove it from the heat and strain it through a fine-mesh sieve to remove the seeds.
3. Set the raspberry sauce aside to cool while you prepare the gelatin. In a separate small bowl, sprinkle the gelatin powder over the water and let it sit for about 5 to 10 minutes to allow it to bloom.
4. After the gelatin has bloomed, stir it into the warm raspberry sauce until fully dissolved. Allow the raspberry mixture to cool to room temperature.

Step 2: Prepare the Cocoa Brownie

1. Preheat your oven to 350°F (180°C) and grease and line an 8-inch (20cm) springform pan with parchment paper.
2. In a medium bowl, whisk the egg and sugar together until smooth. Add the vanilla extract and vegetable oil, whisking until everything is well combined.
3. Sift the flour, cocoa powder, and salt into the egg mixture and stir until fully incorporated.
4. Pour the batter into the prepared pan and spread it evenly.
5. Bake the brownie for 10-12 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs attached. Let it cool completely before moving on to the next step.

Step 3: Prepare the Chocolate Raspberry Crunch

1. While the brownie cools, prepare the crunch layer. Melt the milk chocolate, semisweet chocolate, and butter in a heatproof bowl set over a pan of simmering water (bain-marie). Stir until the mixture is smooth.
2. In a medium bowl, combine the shortbread cookie crumbs, paillete feuilletine, and freeze-dried raspberries (if using).
3. Once the chocolate and butter mixture has melted, pour it over the dry ingredients and mix well to combine.
4. Spread the chocolate crunch mixture evenly over the cooled brownie, leaving a small border around the edges. Refrigerate the cake until the mousse layer is ready.

Step 4: Prepare the Raspberry Mousse

1. In a large mixing bowl, whip the cold whipping cream until stiff peaks form.
2. Add the cooled raspberry mixture to the whipped cream and gently fold them together until fully combined.
3. Line the sides of the springform pan with an acetate sheet for easy removal after the cake has set.
4. Pour the raspberry mousse over the chocolate crunch layer, smoothing the top with a spatula.
5. Refrigerate the cake for at least 4 to 6 hours, or overnight if possible, to allow the mousse to set completely.

Step 5: Prepare the Chocolate Glaze

1. For the glaze, melt the semisweet chocolate and whipping cream together over a bain-marie. Stir until smooth and glossy.
2. Once the mousse has set, remove the cake from the refrigerator. If you used an acetate sheet, gently peel it away from the sides of the cake.
3. Place the cake on a wire rack set over a baking sheet or another pan to catch any drips. Pour the chocolate glaze over the top and allow it to cover the sides of the cake.
4. Use a spatula to smooth out any drips and to decorate the base of the cake with chopped chocolate.
5. Place the cake back in the refrigerator for 20-30 minutes to allow the glaze to set completely.

Step 6: Optional Chocolate Raspberry Shards

1. If you want to add a decorative touch, melt the semisweet chocolate and stir in some tempered chocolate for a smooth finish.
2. Spread the melted chocolate onto a parchment-lined baking sheet and sprinkle it with freeze-dried raspberries and coconut flakes if desired.
3. Refrigerate the chocolate until set, then break it into shards.
4. Decorate the top of the cake with these chocolate shards, fresh raspberries, a dusting of powdered sugar, and fresh mint leaves.