 Chocolate Ganache
Chocolate Ganache2-1/2 lb.'s dark chocolate,  chopped
1-1/4 cups heavy whipping cream
3 tablespoons Cognac
2/3  cup powdered sugar
1 tablespoon cognac
Chocolate  Mayonnaise Cake2- 8" round cake pans, greased and  floured (9" pans can be substituted, the cake will not be as tall  though).
2 cups all-purpose flour
3/4 cup unsweetened cocoa  powder
1- 1/4 teaspoons baking soda
1/4 teaspoon baking powder
1-2/3  cups sugar
3 eggs
1 teaspoon vanilla
1 cup mayonnaise
1-1/3  cup water
edible gold powder
Simple Syrup1/2  cup sugar
1/4 cup water
1/4 cup cognac
Boil sugar, water and  cognac together until sugar dissolves.
Make the cake:
Preheat  oven to 350 F
1. In a medium bowl, whisk together flour, cocoa,  baking soda, and baking powder; set aside.
2. In large mixer bowl  with paddle attachment beat sugar, eggs and vanilla until light and  fluffy on high speed, about 3-5 minutes. Add mayonnaise, reduce speed to  medium and beat a couple of minutes longer.
3. Add flour mixture  to batter, alternating with water- starting and ending with flour. Pour  batter into pans and bake for 30-35 minutes or until cake pulls away  from sides of pan and middle of cake looks set. Leave cake in pan for 10  minutes, then turn out onto a cooling rack.
Make chocolate  ganache:
1. In a large bowl over a double boiler, combine  chocolate, cognac and cream. Whisk until chocolate is melted and all  ingredients are combined.
2. Place about half the chocolate  mixture in the mixer bowl and allow to cool for about 10 minutes. With  the whisk attachment, beat on med-high speed gradually adding 2/3 cup  sifted powdered sugar and an additional tablespoon cognac. Whip until  very light and fluffy. The ganache will have hardened up and should be a  spreading consistency. This will serve as the filling. Set aside until  ready to assemble cake.
3. Whisk remaining ganache (what was left  in the double boiler bowl) occasionally until it hardens up a bit. Set  aside until the cake has completely cooled.
Assembling Cake:
Before  you begin, make sure cake is completely cool- if you rush this process,  everything will melt and you will have a gooey mess. (take my word for  it- I've done it both ways!)
1. With a large serrated knife,  split layers in half and set on a piece of parchment paper. Place the  first layer on a plate at least 3 inches wider than the cake. Place  about 1 cup of the whipped ganache in a pastry bag, set aside. Brush  each layer generously with simple syrup as you add them to the stack.
2.  The first layer will have whipped ganache as filling so spread about a  1/4" layer on. Top with the next layer of cake. Pipe a 1-1/2" tall  "trench" of ganache along the perimeter of the second layer. Add custard  or pastry cream making sure to contain it within the "trench" of  ganache. Add fresh raspberries if desired. Top with third layer and  spread with additional whipped ganache about 1/4" thick- the same as the  first layer. Place top layer on cake and press slightly to seal cake.  You are now done using the whipped ganache. To clarify- All ganache  referred to now will be what was left in the double boiler bowl which  was not sweetened.
3. Place about 1 cup ganache over cake and  spread on top pushing all excess down the sides of the cake, this is the  crumb coat. Any crumbs which come off the cake and stick to the icing  will be covered up with the next coat. Place cake in the refrigerator  for 15 minutes or until icing is set. (do not rush this part- it's so  much easier to do it the right way!)
4. remove cake from  refrigerator, add additional ganache to top of cake spreading with the  spatula until cake is covered and smooth. By this time, ganache should  be fairly stiff- place some in a pastry bag and pipe decoratively on  cake.
5. Place a small amount of gold dust on your hand or small  piece of paper. Blow the powder onto the cake until desired effect is  achieved. Cakes filled with custard or pastry cream must be  refrigerated.
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sourcE: Gourmet Girl