Preheat the oven to 400F and set a rack in the middle. Lightly spray a 12x17 baking sheet with parchment paper (I spray it with a little cooking oil to stick). Butter or slightly spray the parchment liner.

Whisk the eggs, egg yolks, vanilla, salt and sugar together in a large bowl over a pan of simmering water. Whisk gently until the mixture is just lukewarm, about 100F on a candy thermometer (or test with your finger - it should be warm to the touch). Transfer the mixture to the bowl of a stand mixer fitter with the whisk attachment (or hand held beaters) and whip on medium-high speed until the egg mixture is cooled and tripled in volume. The mixture will be thick and will form a slowly dissolving ribbon falling back onto the bowl when the whisk is lifted.

Over a medium bowl or a piece of parchment paper, sift together the flour and cocoa. Add one-third of the flour mixture to the beaten egg mixture. Use a rubber spatula to fold in the flour mixture, making sure to scrape all the way to the bottom of the bowl to prevent the flour mixture from making lumps. Repeat with another third of the flour mixture and finally with the remainder. Pour the batter into the prepared pan and smooth the top with an offset spatula.

Bake the Genoise for about 10 to 12 minutes. Make sure the cake does not over bake and become too dry or it will not roll properly. Let cool on a rack. Remove the cake from the baking sheet and invert it on a larger piece of parchment paper. Peel of the parchment paper that was lining the baking sheet. Set the cake aside.

In a small saucepan set over medium high heat, bring all the ingredients to a simmer until the sugar dissolves, stirring occasionally. Let cool to room temperature.

1.Place toasted hazelnuts in plastic bag and crush with rolling pin.

Combine cream, butter and sugar in small saucepan and bring to gentle boil over medium heat, stirring occasionally. Remove pan from heat and add chopped chocolate, swirling pan to cover chocolate with hot cream. Let stand for 3 minutes to melt chocolate. Gently whisk chocolate mixture until blended. Mix in crushed hazelnuts. Cool slightly before assembling.

Pour 2 tablespoons of the cream into a small heatproof bowl, sprinkle the gelatin over it and let stand until softened, about 10 minutes. Place the bowl in a larger bowl of hot water and stir until the gelatin has dissolved, or. nuke in the microwave for 3 -5 seconds.

Meanwhile, in a saucepan over medium heat, bring the remaining cream, the mascarpone, sugar and salt just to a boil. Remove the pan from the heat, add the chocolate and whisk until smooth.

Add the melted gelatin mixture to the chocolate mixture and stir until well blended. Pour through a fine strainer into a 4-cup glass measuring cup or a bowl.

Cover the panna cotta with plastic wrap and refrigerate until slightly thickened, but not set, about 1 hour or a little less. I let mine set too long, resulting in an uneven layer of panna cotta.

important - Make sure the first layer of genoise is frozen solid and the panna cotta is well- thickened before pouring and spreading it on, or the genoise will absorb half the panna cotta.  Put it right back into the freezer once it's spread evenly.

Set a saucepan with 1 inch of water on low heat. Place eggs white and sugar in mixer bowl and set the bowl over the saucepan as to create a double boiler. Heat the white, while whisking, until the sugar is dissolved and it feels hot to the touch, about 140F.

Transfer the mixture to the bowl of an electric mixer fitted with a whisk attachment. Beat on, medium-high speed until the egg white is stiff, but smooth and glossy, about 8 minutes. Set aside.

In a small bowl, sprinkle the gelatin over 1 tablespoon of the water and 1 tablespoon of the lemon juice and let stand until softened, about 5 minutes. In a blender, puree the blackberries  and raspberries with the remaining 3 tablespoons of water and 1 tablespoon lemon juice.

Strain the blackberry-raspberry puree into a small saucepan; there should be about 1 ½ cups.  Add the remaining sugar and bring to a boil. Simmer the blackberry-raspberry mixture over moderate heat, stirring occasionally, until it is slightly reduced, about 5 minutes. Stir in the softened gelatin until dissolved. Let the mixture cool.   Remove ¾ cup of the puree to a new bowl and stir in ¼ cup water, for the berry mirror.

Beat the heavy cream until you have soft peaks. Fold the Swiss meringue into the cooled berry puree, then fold in the softy whipped cream.

1, Line an 8 inch square pan (preferably 2 to 3 inches deep) with parchment or plastic wrap, making sure paper or wrap extends about 3-inches up the sides over the pan.

Cut out two 8-inch squares of Genoise. Place one square of Genoise on the bottom the lined pan. Brush with simple syrup and freeze for about a half hour.

Remove cake from freezer, and panna cotta from the refrigerator, and pour the panna cotta on top of the frozen Genoise, smoothing it. Top with second square of genoise, and press down evenly. Brush second genoise with simple syrup, and pour the hazelnut ganache on top. Freeze for about 45 minutes to an hour.

Make the berry mousse while ganache is setting. Remove cake from the freezer and pour berry mousse on top of ganache and freeze for another hour, until frozen set.

Stir reserved berry puree or warm gently to loosen it. Remove cake from freezer and pour over the top of the mousse, Chill in the refrigerator until set. I prefer to freeze, then cut, to get nice slices, then bring to room temperature for serving, but since freezing kind of ruins the mirror, chilling in the fridge for the last set is fine. The cake will still be somewhat frozen when cutting, so you'll get nice slices.