Blueberry Custard Cake
For the custard filling:
  • 4 yolks
  • 1 whole egg
  • 3 tablespoons cornstarch
  • ¼ + ¼ cup sugar
  • 2 cups milk
  • ⅛ teaspoon salt
  • 1 teaspoon vanilla extract
  • 2 tablespoons unsalted butter
  • ½ cup heavy cream
  • 3 tablespoons confectioner's sugar
For the blueberry compote:
  • 1 pint fresh blueberries (plus more if you want extra to decorate with)
  • ½ cup granulated sugar
For the cake:
  • ¾ cup buttermilk
  • ½ teaspoon baking soda
  • 1 cup unsalted butter, softened
  • 1½ cups granulated sugar
  • 1 teaspoon pure vanilla extract
  • 2 eggs
  • ⅔ cup blueberry compote
  • ¼ teaspoon salt
  • 5 tablespoons cornstarch
  • 2 cups +3 tablespoons all-purpose flour
For the swiss buttercream:
  • 6 large egg whites (or 170 grams liquid egg whites)
  • 1¼ cups (250 grams) granulated sugar
  • pinch of salt
  • 3 sticks (340 grams) unsalted butter, softened but still cool
  • 4 tablespoons blueberry compote
For the custard filling:
  1. In a medium bowl, whisk together the yolks, egg, cornstarch, and ¼ cup of sugar. Set aside.
  2. In a saucepan, heat the milk, remaining ¼ cup sugar, and salt over medium heat. Stir occasionally and take it off the heat as soon as it starts to boil.
  3. Slowly add ⅓ of the hot milk mixture to the egg mixture, whisking quickly to temper the eggs. Return the tempered egg mixture to the remaining milk mixture in the saucepan and cook, stirring continuously until it reaches a boil. Cook for an additional 2 minutes. Remove from the heat, then stir in the vanilla extract and butter.
  4. Press a layer of cling wrap directly on top of the custard, and refrigerate until cold and firm, at least 2 hours.
  5. Whip the heavy cream and powdered sugar together until it forms firm peaks. Gently fold together the pastry cream and whipped cream together. Press a layer of cling wrap directly on top of the custard cream, and refrigerate until you're ready to use it.
For the blueberry compote:
  1. Heat the blueberries and ½ cup sugar in saucepan over medium heat for 10 minutes, until it thickens. Stir occasionally. Pour into a blender or food processor, and blend until smooth. Cover and cool at room temperature.
For the cake:
  1. Preheat the oven to 350F degrees. Grease two 8'' round baking pans with butter then dust with flour. Line the bottom of baking pans with parchment paper.
  2. In a small bowl, mix together the buttermilk and baking soda, the set aside.
  3. With an electric mixer, mix the butter and sugar on medium speed until smooth, about 3-4 minutes. Add the vanilla extract and eggs, one egg at a time. Continue to mix until incorporated. Stop once or twice to scrape down the sides. Add the buttermilk mixture and ⅔ cup blueberry compote. Slowly add the salt, cornstarch, and flour, and mix until just incorporated (do not overmix).
  4. Evenly distribute the batter into the two prepared cake pans. Wrap the cake pans with baking strips for leveled cakes (optional).
  5. Bake for 34 minutes, until a toothpick inserted in the center comes out clean. Allow the cakes to cool completely before frosting.
For the swiss buttercream:
  1. With an electric hand mixer on medium speed, mix the egg whites and sugar in a glass or steel bowl (e.g. a stand mixer bowl) over simmering water until the egg white mixture reaches 160 degrees F. Take the bowl off the heat.
  2. With an electric mixer on medium-high speed, whip the egg whites until they become fluffy and double in volume.
  3. Allow the egg mixture to cool to room temperature, then add the butter, one stick at a time, and the blueberry compote. Mix until the buttercream is stiff and thick, about 8 minutes. If the mixture is too runny and/or won't thicken up, place the bowl in the refrigerator for about 10-15 minutes, then re-whip until it comes together.
To assemble:
  1. Place ⅓ of the swiss buttercream frosting in a piping bag or gallon-size Ziploc bag. Pipe a thick ring (about ¾ inch thick) of frosting around the circumference of one of the cooled cakes. Fill in the ring with the custard cream (do not overfill), and level with a spatula or butter knife. Place the second layer on top.
  2. Frost the entire cake with the remaining buttercream frosting with an angled spatula, then decorate with the extra blueberries.
Recipe by Sprig and Flours at