Description

This White Chocolate Mousse Cake combines moist white cake layers with a luscious white chocolate mousse filling and a smooth white chocolate buttercream frosting. The cake is made with quality white chocolate, sour cream for moisture, and a delicate balance of sweet and creamy textures. Perfect for special occasions, this elegant dessert delivers a rich but airy experience that delights white chocolate lovers.

Ingredients

Scale

White Chocolate Mousse Filling

1 1/3 cups good quality white chocolate chips (215g)
1 1/2 cups heavy cream or heavy whipping cream, cold – divided (360ml)
1/4 cup powdered sugar (30g)
1 tsp vanilla extract or vanilla bean paste (4ml)
pinch fine salt (less than 1/8 tsp)

White Cake Layers

1 cup (2 sticks) unsalted butter, room temperature (226g)
3 cups granulated sugar (600g)
1 cup carton egg whites or 7 large egg whites, room temperature (235g)
3 cups cake flour (360g)
2 1/2 tsp baking powder (10g)
1 tsp fine salt (6g)
1 1/2 cups full-fat sour cream, room temperature (380g)
1/4 cup vegetable or canola oil (56 ml)
1 tsp vanilla extract or vanilla bean paste (4ml)

White Chocolate Buttercream Frosting

2 cups unsalted butter, room temperature (452g)
7 cups powdered sugar (900g)
1 tsp vanilla extract or vanilla bean paste (4ml)
1/2 tsp fine salt (3g)
1/3 cup heavy whipping cream, room temperature (75g)
1 cup white chocolate chips, melted and cooled (160g)

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Instructions

Make the White Chocolate Mousse Filling: Melt the white chocolate chips with 1/2 cup of heavy cream using a microwave or double boiler until smooth. Set aside to cool slightly. Whip 1 cup of heavy cream with powdered sugar, vanilla extract, and a pinch of salt until soft peaks form. Gently fold half of the whipped cream into the melted white chocolate, then fold in the rest carefully. Cover and refrigerate for at least 2 hours.
Prepare the White Cake Layers: Preheat oven to 325°F. Grease and line four 7-inch or three 8-inch cake pans with parchment paper. Cream butter and granulated sugar on high until light and fluffy. Add egg whites and mix on medium speed. Whisk together cake flour, baking powder, and salt in a separate bowl. Add half dry ingredients to butter mixture on low speed, then sour cream, oil, and vanilla, followed by remaining dry ingredients. Mix until just combined. Divide batter evenly among pans and bake for 37-40 minutes until a toothpick comes out with moist crumbs. Cool for 10 minutes, then chill in freezer for 45 minutes.
Make the White Chocolate Buttercream Frosting: Beat room-temperature butter on low speed until smooth. Add vanilla and salt, then gradually add powdered sugar while mixing. Incorporate heavy cream halfway through to ease mixing. Fold in melted, cooled white chocolate and mix until smooth. Adjust consistency with cream or powdered sugar as needed. Transfer to a piping bag.
Assemble the Cake: Place the first cake layer on a cake board and secure with frosting. Pipe a buttercream ring around edge to form a dam. Spread a layer of chilled white chocolate mousse inside the ring, about 1/3 of mousse per layer for four layers. Stack remaining layers and mousse similarly. Apply a thin crumb coat of frosting and chill until firm. Finish with a thicker layer of buttercream, smooth the sides with an icing comb, and decorate as desired.

Notes

Use high-quality white chocolate for best flavor and smooth texture.
Ensure egg whites and other dairy are at room temperature for proper mixing.
Chilling cake layers before assembly helps prevent crumble and makes frosting easier.
Adjust frosting thickness by adding cream or powdered sugar depending on your climate and preference.
This cake can be refrigerated up to 3 days, or frozen for longer storage.
Be careful folding the mousse to retain its airy texture.