Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan. In a large bowl, whisk together the sugar, flour, cocoa powder, baking powder, baking soda, and salt. Add the eggs, milk, canola oil, and vanilla extract, mixing until smooth. Carefully stir in the boiling water until combined, then pour the batter into the prepared pan. Bake for 25-27 minutes, or until a toothpick inserted comes out clean. Let it cool completely.

While the cake cools, melt the semi-sweet chocolate chips and cream cheese together in a heatproof bowl over simmering water, stirring until smooth. In a separate bowl, soften the unflavored gelatin in cold water. Then, dissolve it in boiling water and set it aside. Whip the heavy cream with powdered sugar until soft peaks form. Gently fold the melted chocolate mixture into the whipped cream, followed by the dissolved gelatin. Spread this rich chocolate mousse over the cooled cake and chill for at least 30 minutes.

For the white chocolate mousse, soften the gelatin in cold water as before. In a small saucepan, boil the heavy cream and pour it over the white chocolate chips, stirring until melted and creamy. Add the softened gelatin and mix until combined. Whip a new batch of heavy cream until soft peaks form, then fold it into the white chocolate mixture. Gently layer this on top of the chocolate mousse. Chill for another 30 minutes to set.

In a small saucepan, bring heavy cream to a gentle boil. Pour it over the remaining semi-sweet chocolate chips in a bowl and whisk until you achieve a glossy ganache. Let the ganache cool slightly until it thickens but is still pourable. Carefully pour the ganache over the layered mousse, ensuring even coverage. Use a spatula to smooth the top if needed.

Once the ganache is set, remove the springform pan gently to reveal the gorgeous layers of your Black Tie Mousse Cake. Decorate the sides with mini semi-sweet chocolate chips by pressing them into the ganache. For a finishing touch, drizzle white candy melts over the top if desired. Refrigerate the assembled cake for at least 4 hours, or overnight for optimal flavor.

When ready to serve, use a hot, dry knife to slice the Black Tie Mousse Cake for clean edges. This decadent dessert is now ready to impress your guests! Enjoy each luxurious bite of this delightful layered masterpiece.