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Blueberry mousse cake on wire rack.

Blueberry Mousse Cake

This amazing Blueberry Mousse Cake is a soft yellow cake covered with light and airy blueberry mousse.
Prep Time 25 minutes
Cook Time 20 minutes
Total Time 45 minutes
Servings 16

Ingredients

For the cake

  • ½ cup (113 g) unsalted butter, softened to room temperature
  • ¾ cup (150 g) granulated sugar
  • 2 large eggs, at room temperature
  • ¾ cup (180 ml) buttermilk, at room temperature
  • 1 tablespoon vanilla extract
  • 1 ½ cups (180 g) cake flour, sifted
  • 1 teaspoon baking powder
  • ¼ teaspoon baking soda
  • ½ teaspoon salt

For the Mousse

  • 16 ounces (453 g) fresh blueberries
  • 2 ¼ teaspoons unflavored gelatin powder, 1 packet
  • 2 tablespoons water, cold
  • ¾ cup (150 g) granulated sugar
  • 1 ½ cups (360 ml) heavy cream, cold
  • ¼ cup (30 g) confectioners' sugar
  • 1 teaspoon vanilla extract
  • fresh blueberries, for garnish

Instructions

Make the cake

  • Preheat the oven to 350°F. Lightly grease one 9-inch square pan. Line the bottom with parchment paper then lightly grease the paper. Set aside.
  • In a large bowl, beat the butter and sugar on medium speed until light and fluffy, about 5 minutes.
  • Add the eggs, one at a time, mixing well after each addition. Beat in the vanilla followed by the buttermilk.
  • Combine the flour, baking powder, baking soda, and salt in a medium bowl. Stir with a whisk and add it to the butter mixture. Beat on low speed just until combined.
  • Spread the batter evenly in the prepared pan. Bake for 20-25 minutes, until a toothpick inserted into the center comes out with few moist crumbs attached. Take care to not over-bake or the cake will be dry.
  • Let the cake cool in the pan for 10 minutes then invert onto a wire rack to cool completely.

Make the Mousse

  • Add the blueberries to a blender or food processor and blend to a thin puree.
  • In a small bowl, mix the gelatin and cold water together. Let it sit while you cook the blueberries.
  • In a medium saucepan, combine the blueberry puree and sugar. Cool over medium heat just until it begins to simmer. Reduce the heat to medium-low and cook for 15-20 minutes, until it has reduced slightly.
  • Add in the gelatin and stir until melted and well combined.
  • Pour the blueberry mixture into a heatproof bowl and place in the refrigerator until completely cool, about 1 hour.
  • In a large bowl, beat the cold cream, confectoiners' sugar, and vanilla at high speed until stiff peaks form.
  • Fold in half the cooled blueberry mixture until almost fully combined. Add the remaining blueberry jelly and fold it in until just combined.
  • Line a clean 9-inch square pan with parchment paper, leaving a 1-inch overhang.
  • Place the cooled cake into the pan. Top with the blueberry mousse.
  • Refrigerate for at least 4 hours.
  • Lift the cake out of the pan by the foil overhang and slice into squares. Garnish each slice with fresh blueberries.

Notes

  • Cake flour: I don't recommend substituting the cake flour in this recipe. It offers a tight crumb that's also very tender and light. You can't replicate this with any other flour.
  • Buttermilk: If you don't have buttermilk, you can make it at home. I have a detailed post on how to make homemade buttermilk.
  • Use fresh summer-ripened blueberries for the best flavor. 
Make ahead tip
  1. The assembled cake will keep for up to 3 days stored in the refrigerator.
  2. The cake layer can be made ahead of time. Wrap the cooled layer tightly in plastic wrap and store it at room temperature for up to 2 days, in the refrigerator for up to 5 days, or in the freezer for up to 2 months. Thaw overnight in the refrigerator.
  3. The blueberry jam mixture can be prepared up to 1 day in advance. Cover tightly and refrigerate until ready to use.