For the chocolate cake layers:

• 1 3/4 cups all-purpose flour
• 3/4 cup unsweetened cocoa powder
• 2 cups granulated sugar
• 2 teaspoons baking soda
• 1 teaspoon baking powder
• 1 teaspoon salt
• 2 large eggs
• 1 cup buttermilk, room temperature
• 1/2 cup vegetable oil
• 2 teaspoons pure vanilla extract
• 1 cup boiling water

For the dark chocolate mousse:

• 8 ounces dark chocolate, chopped
• 1 1/2 cups heavy cream, divided
• 2 tablespoons granulated sugar

For the white chocolate mousse:

• 8 ounces white chocolate, chopped
• 1 1/2 cups heavy cream, divided
• 2 tablespoons granulated sugar

For the milk chocolate mousse:

• 8 ounces milk chocolate, chopped
• 1 1/2 cups heavy cream, divided
• 2 tablespoons granulated sugar

For the ganache topping:

• 6 ounces semisweet chocolate, chopped
• 1/2 cup heavy cream