Step 1: Making the Chocolate Cake Layers

• Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or use parchment paper to line them.
• In a large bowl, sift together the all-purpose flour, unsweetened cocoa powder, granulated sugar, baking powder, baking soda, and salt.
• In another bowl, whisk together the eggs, whole milk, vegetable oil, and vanilla extract until well combined.
• Add the wet ingredients to the dry ingredients gradually, mixing until just combined. Be careful not to overmix.
• Gently stir in the boiling water. The batter will be thin, which is normal.
• Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
• Let the cakes cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

Step 2: Making the White Chocolate Mousse

• In a heatproof bowl, melt the chopped white chocolate over a pot of simmering water or in the microwave in 30-second intervals, stirring until smooth. Let it cool slightly.
• In a mixing bowl, whip 1 cup of heavy cream with a hand mixer or stand mixer until stiff peaks form.
• Fold the melted white chocolate and vanilla extract into the whipped cream until well mixed.
• Refrigerate the mousse for at least 1 hour to set.

Step 3: Making the Dark Chocolate Ganache

• In a saucepan, heat 1 cup of heavy cream until it just begins to simmer.
• Place the chopped dark chocolate in a heatproof bowl. Pour the hot cream over the chocolate and let it rest for 2-3 minutes.
• Stir until the chocolate is completely melted and the ganache is smooth. Let it cool slightly before using.

Step 4: Making the Vanilla Buttercream

• In a mixing bowl, beat the softened butter with a hand mixer or stand mixer until creamy and smooth.
• Slowly add the powdered sugar, mixing on low speed to prevent a cloud of sugar.
• Once the sugar is incorporated, add the heavy cream, vanilla extract, and a pinch of salt. Whip on high speed until the buttercream becomes light and fluffy.

Step 5: Assembling the Cake

• If the cakes have domed tops, level them with a knife or cake leveler.
• Set one cake layer on a serving plate or cake board. Spread a layer of white chocolate mousse over the cake.
• Add the second cake layer on top of the mousse.
• Apply a crumb coat (a thin layer of buttercream) over the entire cake. Chill for 30 minutes to set.
• Frost the cake with the remaining vanilla buttercream. Smooth it out or create desired decorations.
• Pour the slightly cooled dark chocolate ganache over the top of the cake, letting it drip down the sides.
• Chill the cake for at least 1 hour before serving to let the mousse and ganache set properly.

Enjoy your luxurious Tuxedo Cake, a delightful combination of chocolate and vanilla that is sure to impress at any gathering!