1. Prepare the Chocolate Cake:

• Preheat the oven to 350°F (180°C) and grease two 8-inch round cake pans.
• In a large bowl, sift together the dry ingredients: flour, sugar, cocoa powder, baking powder, baking soda, and salt.
• In another bowl, whisk the wet ingredients: milk, eggs, sour cream, vegetable oil, vanilla extract, and espresso powder.
• Combine the wet and dry mixtures, mixing until just combined.
• Gradually add the hot water, mixing until the batter is smooth.
• Divide the batter evenly between the prepared cake pans and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
• Let the cakes cool completely in the pans before removing.

2. Prepare the Chocolate Mousses:

• In a saucepan over medium-low heat, warm half of the heavy cream and vanilla extract until it just begins to steam.
• In a separate bowl, whisk the egg yolks with sugar and cornstarch until pale and slightly thickened.
• Gradually pour the warm cream into the egg mixture, whisking continuously to temper the eggs.
• Return the mixture to the saucepan and cook over medium heat, stirring constantly until it thickens.
• Divide the custard into two bowls.
• Add the dark chocolate to one bowl and the white chocolate to the other, stirring until each is completely melted and smooth.
• In separate bowls, whip the remaining heavy cream until stiff peaks form.
• Gently fold half of the whipped cream into each chocolate mixture until combined.

3. Assemble the Tuxedo Cake:

• Place a dessert ring on a serving plate and trim the tops of the cooled cake layers to make them level.
• Place one cake layer into the dessert ring.
• Spread the dark chocolate mousse evenly over the cake.
• Add the white chocolate mousse on top of the dark chocolate mousse.
• Place the second cake layer on top of the mousse.
• Refrigerate the assembled cake for at least 4 hours until the mousse is set.

4. Prepare the Chocolate Ganache:

• Heat the heavy cream in a saucepan over medium heat until it just begins to steam.
• Pour the hot cream over the chopped milk chocolate and let it sit for 1 minute.
• Stir until the ganache is smooth and glossy.
• Pour the ganache over the top of the cake, allowing it to drip down the sides.
• Let the ganache set before removing the dessert ring.