Before anything else, make sure to prepare and cut your cooled marble cake into layers of choice.
After that, in a mixing bowl, whisk the cocoa powder and hot water. Afterward, set it aside.
Then, in a heat-proof bowl, add the chopped chocolate compound. After that, please place it in the microwave for twenty seconds, stir in the melted chocolate using a rubber spatula. If it’s not as melted, you can add a few seconds more.
Then, pour the cocoa water mixture into the melted chocolate and whisk until completely incorporated.
Afterward, prepare a hand or stand mixer fitted with a wire whisk attachment. Then, whip the heavy whipping cream for two minutes at high speed until it becomes smooth. Next, turn the mixer to low. Then, add the confectioners’ sugar to the mixer. After that, at medium-high speed, add the vanilla. Make sure to beat for three minutes or until the cream is at a medium peak.
Next, pour in the chocolate mixture and cautiously fold it in together. Make sure not to over-mix because it can cause the mousse to deflate.
Finally, cover the mouse and let it chill in the refrigerator for an hour or until needed.