Stir sugar and 1/3 cup water in a small saucepan over medium heat until sugar dissolves.  Increase to high heat and cook without stirring until light amber in color, about 6 minutes.  Stir in hazelnuts, then pour onto a parchment lined sheet tray, separating nuts.  Let cool.

Transfer candied nuts to a food processor. Add vegetable oil and puree until smooth to make praline paste.

Place both chocolates and 4 Tbsp of praline paste in a medium bowl. Reserve remaining praline paste for mousse. Set bowl over a saucepan of simmering water (bain-marie) and stir until chocolate is melted and the mixture is smooth.

Remove from heat and stir in salt and cereal. Spread out a thin layer (between 1/8” to 1/4”) on a parchment lined sheet tray. Chill until set, about 20-30 minutes.

Preheat over to 375 degrees F.  Line a 17x11x1” sheet pan with a butter parchment paper.

Sift together flour and cocoa powder twice and set aside.

Separate 4 eggs, placing yolks in a large bowl and whites in a medium bowl. Beat yolks with 1/2 cup sugar on medium speed in a stand mixer until thick and pale in color. Add the remaining whole eggs, one at a time, blending well between additions.

In another bowl, beat egg whites with remaining 1/2 cup sugar and corn syrup until slightly thickened and frothy. Add egg whites to yolk mixture and beat to beat.

Add flour-cocoa mixture and fold to blend. Spread out on prepared baking sheet. Bake for 15 minutes or until toothpick inserted into center of cake comes out clean. Let cool completely and then invert cake a peel off parchment. Brush cake with brandy.

Bring cream to a boil in a small saucepan. Puree hot cream, ground hazelnuts, and salt in a food processor.  Let cool to room temperature.

With machine running, add butter 1 tablespoon at a time. Puree until smooth. Cover and chill until ready to use. Return to room temperature before use.

Combine chocolate, praline paste, and butter in a medium bowl.

Bring 3/4 cup cream to a boil and pour over chocolate mixture. Let stand for 1 minute before stirring. Stir until melted and mixture is smooth.

Beat remaining cup of chilled cream to soft peaks. Fold whipped cream into slightly cooled chocolate mixture. Cover and chill until ready to use.

Spread hazelnut ganache over soaked cake and chill in freezer for 15 minutes.

Spread praline mousse over set ganache and chill in freezer for another 15 minutes until set.

Cut cake crosswise into thirds. Stack layers on top of each other. Trim edges. Place in refrigerator and chill overnight.

Let cake stand at room temperature for 15 minutes before serving. Break up praline chocolate crunch into large shards and arrange on top of cake.