White Chocolate Mousse Cake

Simple and divine white cake filled with decadent white chocolate mousse and frosted in classic vanilla buttercream.

3 sticks (or 1 1/2 cups) unsalted butter left out at room temp for 10-15 minutes
1 pinch salt
1 Tablespoon pure vanilla
1/4 cup heavy cream (plus more later for thinning)
7 cups powdered sugar

Preheat the oven to 325 degrees, then prep three 6” cake rounds with a swipe of shortening and dust of flour to prevent sticking. Set aside.
In a large mixing bowl, hand whisk together the buttermilk, sour cream, eggs, oil, and vanilla until thoroughly combined. Sift in the cake mix and whisk until just combined. Do not overmix. Next, split the batter evenly between the prepared cake rounds.
Bake for 27-30 minutes until the center is baked through. Remove cake rounds from the oven, then let the cakes cool in the pan for a minute before flipping them out onto a wire rack to cool completely. Wrap and chill cakes flat before assembly.

Follow the instructions for my White Chocolate Mousse and set aside. (https://bakingwithblondie.com/easy-white-chocolate-mousse/)

In the bowl of a stand mixer fitted with a paddle attachment, whip up the butter until it’s light and fluffy. Add in the salt, vanilla bean, and heavy cream. Whip up to combine and then scrape down the sides with a spatula.
With the stand mixer on low speed, add in the powdered sugar about a half cup at a time. It will be thick. Add in a little more heavy cream to thin it out if needed (1 Tablespoon at a time), and then flip the mixer on high speed for 2 minutes to lighten the color and texture of the buttercream.

Place a cardboard cake round on a cake turntable.
Spread on a little bit of buttercream in the center of the round with an angled icing spatula.
Place down the first chilled cake layer in the center. Add on a thin layer of buttercream on top and smooth it out with an angled icing spatula again.
Pipe a dam of vanilla buttercream around the outside rim of the cake layer, then pipe in the white chocolate mousse in the center.
Place the next cake layer on top, then repeat with the rest of the layers - making sure to line the layers up evenly. After adding on the top cake layer, crumb coat the cake by spreading the buttercream in a thin layer around the entire cake. Freeze for 2 minutes to set.
Using a wooden spoon, hand-beat out any air bubbles in the remaining buttercreams. Spread on a final layer of white buttercream around the entire cake, using a cake scraper for clean edges and sides.
Using a small petal #102 piping tip going vertically, pipe a small herringbone pattern from top to bottom. Repeat around the sides of the cake (you can use a cake scraper to carefully press and indent where you want the lines to go to ensure more straight lines and a good guide as you're piping).
With a large pedal piping tip #124, pipe a herringbone pattern crown around the top rim of the cake.
Enjoy!