For cake: Preheat oven to 350 deg f. Prepare a cake pan or springform pan by greasing it and then dusting it with flour. Shake of excess flour.
In a mixing bowl, combine flour, cocoa powder, sugar, baking powder, and salt.
In another small bowl, combine eggs, milk, vanilla, and oil. Whisk till its smooth.
Add the wet ingredients to the dry ingredients. Mix again. Add baking soda and stir.
Add boiling water to the batter and mix well.
Pour the batter in the cake pan and spread it out evenly. Wrap a wet napkin around the cake pan tying it securely with a pin or use readymade cake wrap.
Bake for 30-35 minutes or until toothpick when inserted in the cake comes out clean.
Remove from oven and let the cake cool down completely. Cut the cake in half (use dental floss for precision).Bake for 30-35 minutes or until toothpick when inserted in the cake comes out clean
For the Mousse:. Prepare a double boiler. Heat a saucepan with water and bring it to a boil. Lower temperature and place a heat resistant container with chocolate over the saucepan taking care the water does not touch the base of the upper bowl.
Add sugar, coffee, and butter to the melting chocolate. Whisk to get a smooth texture. Leave it aside to cool completely at room temperature.
Whip the heavy cream with handheld mixer till stiff peaks are formed (may take around 3-4 minutes).
Gently fold the cream into the chocolate and keep folding and cutting the mixture till its one homogenous mix and color. Cool in refrigerator for at least 30 minutes.
For chocolate ganache: Placing the chocolate in microwave safe bowl, melt it at intervals of 15 seconds stirring each time.
Add warm heavy cream in to the chocolate and whisk to form a thick chocolate syrup. Once it cools, the ganache will thicken.
Assembly: Place one cake half on a wire rack. Ladle the Mousse onto the cake and spread it out evenly. Place the other half of cake over the Mousse.
Apply the chocolate ganache over the entire cake and make it as even as as possible.
Decorate with additional chocolate pieces or chocolate shavings or raspberries.