Preheat the oven to 350 degrees F. Grease and flour a 10-inch bundt cake mold.
Place the water, sugar, cocoa powder, baking powder, eggs, and vanilla in a large bowl and stir until well blended
In a medium saucepan over medium heat, stir 1/4 cup of the hot water with the gelatin until all of the gelatin is completely dissolved.
Pour the cake batter into your bundt pan and bake for 30 minutes or until a toothpick inserted in the middle comes out clean.
In a medium bowl, combine the gelatin and hot water again, stir until completely dissolved, and set aside to cool to room temperature.
In a small bowl, beat the sour cream, sugar, and vanilla until blended. Beat in the cooled gelatin mixture until well blended.
Spread the cold cake with a layer of chocolate mousse, then refrigerate for 15 minutes or until it sets.
Spread another layer of chocolate mousse on top of the cake and refrigerate for 30 minutes or until set.
Spread the whipped cream frosting on top of the cake and garnish it with a black chocolate wave.