Chocolate Genoise: Preheat your oven to 350 degrees F (180 degrees C). Butter, or spray with a non stick spray, two - 9 inch (23 cm) round cake pans and line the bottoms of the pans with parchment paper.
Sift the flour with the salt and cocoa powder.
In a heatproof bowl (preferably stainless steel) whisk together the eggs and sugar. Place the bowl over a saucepan of simmering water. Whisking constantly, heat the eggs and sugar until lukewarm to the touch (this will take about 3 - 5 minutes). Remove from heat and transfer the mixture to the bowl of your electric mixer, fitted with the whisk attachment (or with a hand mixer). Beat on high speed until the egg mixture has cooled, tripled in volume, and looks like softly whipped cream (the batter will fall back into the bowl in a ribbon-like pattern). (This will take about 3-5 minutes.) Beat in the vanilla extract. Then sift about one-third of the flour mixture over the whipped eggs and gently fold in using a spatula. Fold in half of the remaining flour, and then fold in the rest.
Take about 1 cup (240 ml) of the batter and fold it into the hot butter. (This lightens the butter.) Then, with a spatula, gently fold the butter mixture completely into the egg batter. Evenly divide the batter between the two pans (about 340 grams in each pan), smoothing the tops with an offset spatula or the back of a spoon. Bake until the cakes shrink slightly from the edges of the pans and the tops spring back when lightly pressed (about 15 - 18 minutes). (A toothpick inserted into the center of the cake comes out clean.) Cool completely in their pans that have been placed on a wire rack. To remove the cakes from their pans, run a small knife around the edges to release the cake. If not using right away, the cakes, well wrapped, will keep two days in the refrigerator or they can be frozen for a couple of months.
Soaking Syrup: Place the water and sugar in a small saucepan and bring to a boil. Let the mixture boil for about one minute or until the sugar dissolves. Remove from heat and let cool to room temperature. Stir in the Grand Marnier (or orange juice). The sugar syrup can be made, covered, and stored in the refrigerator for a couple of weeks.
Chocolate Mousse: In a heatproof bowl (preferably stainless steel), set over a saucepan of simmering water, melt the chocolate. Remove from heat and let cool slightly.
In the bowl of your electric mixer, fitted with the whisk attachment (or with a hand mixer or wire whisk), whip the heavy cream with the sugar until soft peaks form. Then whisk or fold about one quarter of the whipped cream into the melted chocolate. (Do this quickly so the chocolate does not seize (become grainy).) Then gently fold or whisk the rest of the whipped cream (in two to three stages) into the chocolate. Place the chocolate mousse in a piping bag fitted with a 1/2 inch (1.25 cm) plain tip.
Place one cake layer (top of the cake facing down) on a 9 inch (23 cm) cake circle and then place on a cake turntable or your serving plate. (See video for demonstration.) With a pastry brush, moisten the cake with some of the soaking syrup. Next, evenly spread the raspberry jam over the cake. Pipe the chocolate mousse in concentric circles on top of the raspberry jam. (If there is any leftover Chocolate Mousse place in a bowl, cover, and refrigerate. It will be used to garnish the top of the cake.)
Next, brush the top side of the second layer of genoise with the soaking syrup. Then place the cake layer, top side down, on top of the filling. Gently press the top of the cake to compact. Brush the top of the cake with soaking syrup. Smooth the sides of the cake with a spatuala. Cover and refrigerate several hours, or preferably overnight, until firm. (This will ensure that the Ganache will not lose its shine when the cake is stored in the refrigerator.)
Chocolate Ganache: Place the chopped chocolate in a medium sized heatproof bowl. Heat the cream and butter in a small saucepan over medium heat. (Can also heat the cream and butter in the microwave.) Bring just to a boil. Immediately pour the boiling cream over the chocolate and allow to stand, without stirring, for a few minutes. Stir gently (as you do not want to incorporate air into the ganache) with a spoon or whisk until smooth.
Place the cake on a wire rack, and put the wire rack on top of a large baking sheet (to catch any excess ganache that drips from cake.) Then pour the Ganache over the top of the cake. Working quickly, spread the Ganache with a metal spatula or knife, using big strokes to push the ganache over the sides of the cake. (This will create an even coating of ganache.) (See video for demonstration.) Place the cake in the refrigerator until the Ganache has set (about 30 minutes). Then place any leftover Chocolate Mousse in a piping bag fitted with a star tip (I used a Wilton 1M). Pipe swirls on top of the Chocolate Ganache. The cake can be covered and stored in the refrigerator for several days. Bring to room temperature before serving. Well wrapped, this cake can also be frozen for about one month. Defrost in the refrigerator overnight.