Preheat your oven to 350ºF (180ºC) and prepare a 9-inch springform pan.

Whisk the dry ingredients together in a large mixing bowl.

Combine the wet ingredients in another bowl and mix until smooth.

Incorporate the dry mixture into the wet ingredients until just combined.

Carefully add boiling water to the batter and mix gently.

Pour the batter into the prepared springform pan and bake for 24-28 minutes.

Let the cake cool in the pan for about 15 minutes and then transfer to a wire rack.

Prepare the mousse by whisking ingredients and heating until 170ºF.

Stir in chopped dark chocolate until melted and smooth.

Whip cream and fold into the chocolate mixture to create the mousse.

Spread the mousse atop the cooled cake and chill for at least 8 hours.

Make the ganache by heating heavy cream and pouring it over dark chocolate until smooth.

Pour the ganache over the chilled mousse layer and allow to set.

Slice and serve the cake, optionally garnishing with fresh berries.