Prepare chocolate cake according to directions. Cut off the skin from the top of the cake and slice off the top to level at the same time if necessary. You will need to make three cuts using a slicing knife to transfer the cut layers of cake.
In a saucepan, combine the sugar, water and Kahlúa over medium-high heat and bring to a boil, stirring occasionally until the sugar is dissolved. Continue cooking without stirring until the mixture is the consistency of syrup, about five minutes longer. Set aside to cool to room temperature.
Place a large bowl of iced water near the stove. In a saucepan, combine the chocolate and heavy cream over medium heat until the chocolate begins to melt and the cream is almost simmering. Whisk or stir until the chocolate and cream are smooth. Stir in the vanilla and powdered sugar. Remove from the heat and place the pan in the bowl of ice water. Whisk until the mixture is creamy smooth and softly holds its shape. Spoon into a serving bowl and chill for two hours.
To assemble, brush each layer evenly with simple syrup. Next, smooth on chocolate mousse until you have assembled a three-layer cake. With the ganache, frost top of the cake, just enough to cover, and use the remaining to cover the sides of the cake.
Serve with whipped cream, chocolate syrup and cherry.