White Chocolate Cake

Make the cake: Adjust racks to center and lower-third position, and preheat oven to 350°. Line 3, 8” cake pans with parchment, and grease with cooking spray. Place chocolate in a heat-safe bowl and set over a pan of simmering water, ensuring bottom of bowl doesn’t touch water. Stir until chocolate is completely melted and smooth. Remove from heat and let cool to room temperature.  In a large bowl, whisk together flour, baking powder, and salt.  In another large bowl using a hand mixer, or in the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition, then add vanilla. Add half of the dry ingredients and beat until just a few dry streaks remain. Add milk and sour cream, and beat until incorporated. Add remaining dry ingredients and beat until just combined. Divide batter evenly between cake pans, and smooth tops with an offset spatula.  Bake until a toothpick inserted in middle comes out clean, 28 to 30 minutes. Let cool 10 minutes, then invert onto a cooling rack and let cool completely. Make the mousse: Place chocolate in a small heat-safe bowl. In a small pot over medium heat, heat ¼ cup cream until simmering. Pour over chocolate and let sit for 1 minute, then stir until smooth. Refrigerate to let cool completely, about 10 minutes. Give the mousse a stir after about 5 minutes to make sure the chocolate isn’t hardening.  Meanwhile, place remaining ¾ cup heavy cream in bowl of a stand mixer fitted with the whisk attachment, and beat until stiff peaks form. Gently fold in cooled chocolate mixture until just combined. Make the frosting: In a large bowl using a hand mixer, or in bowl of a stand mixer fitted with the paddle attachment, beat cream cheese and butter until smooth. Add powdered sugar and beat until no lumps remain, then add in vanilla. Make ganache: Place chocolate in a small heat-safe bowl. In a small pot over medium heat, heat ¼ cup cream until simmering. Pour over chocolate and let sit for 1 minute, then stir until smooth. Assemble cake: Using a large serrated knife, level tops of cakes as needed. Place one layer on a serving dish, and top with half of the mousse. Smooth into an even layer. Top with a second layer of cake, then remaining mousse. Top with third layer of cake.  Frost top and sides with cream cheese frosting, reserving some to pipe onto top of cake, if desired. Spoon ganache over top of cake, and let drip down the side.  If desired, place reserved frosting into a pastry bag with a large open star tip, and pipe dollops around edge of cake. Sprinkle top with chocolate shavings.