1. Preheat your oven to 350°F. Grease and line three 9-inch round cake pans with parchment paper. In a large bowl, whisk together the flour, sugar, cocoa powder, baking powder, and salt. In a separate bowl, beat the butter until smooth, then add the egg whites, buttermilk, oil, vanilla, and espresso (if using), and mix until well combined. Gently fold the wet ingredients into the dry ingredients, being careful not to overmix. Divide the batter evenly among the prepared pans and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in the pans for 10 minutes, then invert them onto a wire rack and let them cool completely.

2. In a double boiler or a heatproof bowl set over a saucepan of simmering water, melt the white-chocolate chips with the 1/3 cup of warm water, stirring occasionally until smooth. Allow the mixture to cool to lukewarm. In a chilled bowl, whip the 1 1/3 cup of heavy cream with the powdered sugar until soft peaks form. Gently fold the melted white-chocolate mixture into the whipped cream until fully incorporated. Chill the white-chocolate mousse for at least 2 hours.

3. In a double boiler or a heatproof bowl set over a saucepan of simmering water, melt the dark-chocolate chips with the remaining warm water, stirring occasionally until smooth. Allow the mixture to cool slightly. In a chilled bowl, whip the 1 cup of heavy cream with the powdered sugar until soft peaks form. Gently fold the melted dark-chocolate mixture into the whipped cream until fully combined. Chill the dark-chocolate mousse for at least 2 hours.

4. In a small saucepan, heat the 3/4 cup of heavy cream over medium heat until it just begins to simmer. Remove the pan from the heat and pour the hot cream over the 1 cup + 1 tablespoon of dark-chocolate chips. Let the mixture sit for 2 minutes, then stir until the chocolate is completely melted and the ganache is smooth. Add the butter, corn syrup, and salt, and stir until well combined. If the ganache is too thick, you can add a small amount of warm cream to adjust the consistency.

5. Level the three chocolate cake layers to ensure they are flat and even. Place the first layer on a cake stand or serving plate. Spread the white-chocolate mousse evenly over the top. Add the second cake layer and spread the dark-chocolate mousse over it. Top with the third cake layer. Chill the assembled cake for about 15 minutes to firm up the layers.

6. Next, pour the chocolate ganache over the center of the cake, allowing it to drip down the sides. Use a spatula or the back of a spoon to help guide the ganache and create a smooth, even coating.

7. Refrigerate the Perfect Chocolate Tuxedo Cake for about 1 hour to allow the ganache and mousse layers to set. When ready to serve, use a hot, clean knife to slice the cake, wiping the blade between cuts for clean, professional-looking slices.