Preheat the oven to 350°F.

Line a 9” springform pan with parchment paper and set aside.

In a large bowl, whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt.

Add the melted butter, buttermilk, egg, vanilla, and warm water. Mix until combined.

Pour the batter into the prepared pan.

Bake for 45 minutes or until a toothpick comes out clean. Let it cool.

In a double boiler, melt the chopped dark chocolate, butter, and Kahlua over medium heat. Set aside to cool slightly.

In a stand mixer, whip the egg whites on medium speed until foamy. Gradually add the sugar and whip until medium peaks form.

Bloom the gelatin in the water for at least 5 minutes.

Whip the egg yolks until pale and fold them into the chocolate mixture.

Warm 1/2 cup of heavy cream and mix in the gelatin. Fold this into the chocolate mixture.

Fold the whipped egg whites into the chocolate mixture.

Whip the remaining 1 cup of heavy cream to soft peaks and fold into the chocolate mixture.

Pour the mousse over the cooled cake in the springform pan. Spread evenly and cover with plastic wrap. Chill for at least 4 hours or overnight.

Place the chopped chocolate, butter, vanilla, and salt in a bowl.

Heat the heavy cream until just before boiling and pour over the chocolate mixture. Let sit for 2 minutes, then stir until smooth.

Let the ganache cool slightly, then pour over the chilled mousse cake. Chill for about 30 minutes until set.

Run a knife along the edges of the springform pan and remove the outer ring.

Slice and serve the cake.