Preheat the oven to 350 degrees Fahrenheit.

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

In a large mixing bowl, combine the flour, cocoa powder, sugar, baking soda, baking powder, and salt. Mix with a whisk to evenly combine.

Add the melted butter, buttermilk, egg, vanilla, and warm water. Mix with a whisk until the ingredients are evenly combined.

Add the chopped dark chocolate, butter, and Kahlua into a bowl. In a double boiler over medium heat, melt together the mixture. (This can also be done in a microwave in 30-second intervals). Set aside to cool slightly.

In a stand mixer or with a hand mixer, add the egg whites and whisk together on medium speed until just foamy. After the egg whites are foamy, add in the sugar and whip until medium peaks form.

Add the gelatin to the water. Mix to combine and set aside to bloom for at least 5 minutes.

While the gelatin is blooming, whip the egg yolks in a bowl with a hand mixer or the base of a stand mixer until they are pale in color. Fold the whipped egg yolks into the chocolate mixture.

After the yolks are added, heat ½ cup of heavy cream in the microwave until warm but not boiling. Add the gelatin-water mixture to the warmed cream and mix to combine. Fold the mixture into the chocolate mixture.

After the gelatin is added, fold the whipped egg whites into the chocolate mixture

Lastly, whip the remaining 1 cup of heavy whipping cream until soft peaks form. Fold the whipped cream into the chocolate mixture until combined.

Pour the mousse over the cooled cake into the springform pan. Spread into an even layer so the top is flat. Cover with a piece of plastic wrap to set for at least 4 hours or overnight.

In a medium bowl, add the chocolate, butter, vanilla, and salt. Set aside.

Heat the heavy whipping cream until hot but just before boiling. Pour the hot cream over the bowl of chocolate, butter, vanilla, and salt. Let it sit for 2 minutes before stirring.

After 2 minutes, stir until smooth. If any pieces of butter or chocolate remain, heat in the microwave for 30-second intervals until just melted (the goal is for it to be just melted, not too hot as it will melt the mousse).

After the mixture is smooth, remove the cake from the fridge and remove the piece of plastic wrap. Pour the ganache over the cake and let it set in the fridge for about 30 minutes or until the ganache is set.

When ready to serve, gently run a knife along the edges of the springform pan. Remove the outer ring from the pan before slicing and serving.