Description

This White Chocolate Mousse Cake is a decadent and elegant dessert perfect for special occasions. It features moist, tender white cake layers layered with a creamy white chocolate mousse and finished with a luscious white chocolate buttercream frosting. The mousse adds a light, airy texture while the buttercream provides rich sweetness and smoothness, making this cake both visually stunning and irresistibly delicious.

Ingredients

Scale

White Chocolate Mousse

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 Recipe

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: Begin by melting the white chocolate chips with 1/2 cup of heavy cream in a medium-sized heat-proof bowl using the microwave for 60-75 seconds or a double boiler. Stir until smooth and set aside to cool slightly. In a separate large bowl or stand mixer fitted with a whisk attachment, whip 1 cup of heavy cream with powdered sugar, vanilla extract, and a pinch of fine salt on medium-high speed until soft peaks form, about 2 1/2 to 3 minutes. Fold half of the whipped cream gently into the cooled white chocolate mixture, then fold in the remaining whipped cream carefully to avoid deflating the mousse. Cover with plastic wrap and refrigerate for at least 2 hours to chill.
Prepare the White Cake Layers: Preheat your oven to 325°F. Grease and line four 7-inch or three 8-inch cake pans with parchment paper. Using a stand mixer with a whisk attachment, cream the unsalted butter and granulated sugar on high until light and fluffy. Add the egg whites at medium speed and incorporate completely. In a separate bowl, whisk together cake flour, baking powder, and salt. Add half of the dry ingredients to the butter mixture on low speed, followed by sour cream, oil, and vanilla, then the remaining dry ingredients; mix just until combined. Divide the batter evenly among pans, weighing cakes for even layers, then bake for 37-40 minutes until a toothpick comes out with moist crumbs. Cool for 10 minutes in pans, then loosen edges with an offset spatula and transfer to a freezer for 45 minutes to chill completely.
Make the White Chocolate Buttercream Frosting: While cake bakes and cools, beat room-temperature butter on low speed until smooth. Add vanilla extract and salt, then gradually add powdered sugar mixing on low speed. Incorporate heavy cream halfway through to ease mixing. Fold in melted, cooled white chocolate and continue mixing until the texture is smooth and fully combined. Adjust thickness by adding cream or powdered sugar as needed. Transfer frosting to a piping bag and seal.
Assemble the Cake: Place the first cake layer on a greaseproof cake board, secured with a dab of frosting. Pipe a ring of buttercream around the edge to create a dam, then spread an even layer of chilled white chocolate mousse inside the ring using about 1/3 of the mousse for four layers or 1/2 for three layers. Repeat by stacking remaining layers and mousse. Apply a thin crumb coat of frosting to cover the cake entirely. Chill in refrigerator for 30 minutes or freezer for 10 minutes until firm. Apply a final thicker layer of white chocolate buttercream and smooth the sides using an icing comb and bench scraper. Decorate with buttercream swirls and sprinkles as desired.

Notes

Chill the mixing bowl and whisk attachment before whipping the cream for mousse to speed up the process and improve texture.
Measure flour accurately by spooning into the cup and leveling or ideally use a kitchen scale.
Mix cake batter only until ingredients are just incorporated to ensure tender, fluffy cake layers.
Use a kitchen scale to weigh cake batter in pans for uniform layers that bake evenly.
Tap cake pans on the countertop before baking to release trapped air bubbles.
Level cake layers with a serrated knife at room temperature or when thawed for easier stacking and even layering.
Freeze leveled cake layers before assembling to ease handling and prevent sliding while frosting.
Make cake layers and frosting ahead of time and store properly to streamline assembly.
Store leftover frosting airtight in the refrigerator for up to one month or freeze for up to three months; stir well after thawing.
White chocolate mousse filling can be prepared up to two days in advance and refrigerated.
Frosted cake can be stored in the fridge for up to one week or frozen for up to one month, maintaining freshness and moisture.
Use leftover frosting to cover any exposed cut cake surfaces to keep them moist when storing refrigerated leftovers.

Nutrition

Serving Size: 1 slice (approx. 1/24th of cake)
Calories: 420 kcal
Sugar: 35 g
Sodium: 150 mg
Fat: 28 g
Saturated Fat: 17 g
Unsaturated Fat: 8 g
Trans Fat: 0.5 g
Carbohydrates: 38 g
Fiber: 0.5 g
Protein: 4 g
Cholesterol: 95 mg