Lemon Blueberry Cake with Lemon Buttercream

For the Cake:

• ½ cup whole milk (120 ml), room temperature
• ½ cup sour cream (120 g), room temperature
• 3 egg whites, room temperature
• 3 tablespoons fresh lemon juice
• 1 tablespoon lemon zest
• 1 tablespoon vanilla extract
• 2 cups all-purpose flour (240 g)
• 1⅔ cups granulated sugar (333 g)
• 1½ teaspoons baking powder
• ¼ teaspoon kosher salt
• ¾ cup unsalted butter (170 g), room temperature
• 1⅓ cups fresh blueberries (180 g)

For the Blueberry Reduction:

• 1½ cups fresh blueberries (200 g)
• 1 tablespoon granulated sugar
• 1 tablespoon fresh lemon juice
• 1 tablespoon water

For the Lemon Buttercream:

• 1½ cups unsalted butter (340 g), room temperature
• ¼ teaspoon kosher salt
• 6 cups confectioners’ sugar (720 g)
• 3 tablespoons fresh lemon juice

Directions

1. Preheat the Oven:
   Preheat your oven to 350°F (175°C). Grease and flour three 6-inch round cake pans. For more even baking, you can wrap the outsides of the pans with damp fabric cake strips.
2. Prepare the Wet Ingredients:
   In a medium bowl, whisk together the milk, sour cream, egg whites, lemon juice, lemon zest, and vanilla extract. Set aside.
3. Mix the Dry Ingredients:
   In a separate medium bowl, sift together the flour, sugar, baking powder, and salt. Remove 1 tablespoon of the flour mixture and toss it with the blueberries in a small bowl to coat the berries. Set aside.
4. Prepare the Cake Batter:
   In a large mixing bowl or stand mixer fitted with the paddle attachment, beat the softened butter on medium speed until creamy, about 1 minute. Add the dry ingredients and beat on low speed until the mixture resembles coarse sand.
5. Add the Wet Ingredients:
   With the mixer running on low speed, slowly pour in the wet ingredients and mix until the batter is smooth and fully combined.
6. Fold in the Blueberries:
   Gently fold the flour-coated blueberries into the batter using a spatula.
7. Bake the Cake:
   Divide the batter evenly between the prepared cake pans. Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center of the cakes comes out clean. Allow the cakes to cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.
8. Make the Blueberry Reduction:
   In a small saucepan, combine the blueberries, sugar, lemon juice, and water. Cook over medium heat for 5-7 minutes, stirring occasionally, until the blueberries have burst and the mixture has thickened. Remove from heat and let it cool.
9. Prepare the Lemon Buttercream:
   In a large bowl, beat the softened butter with the salt until smooth. Gradually add the confectioners’ sugar, 1 cup at a time, and continue to beat until fluffy. Add the lemon juice and beat until fully incorporated.
10. Assemble the Cake:
    Once the cakes have cooled, spread a layer of lemon buttercream on top of the first cake layer. Add a few spoonfuls of the blueberry reduction on top. Repeat with the second layer. Finish by frosting the top and sides of the cake with the lemon buttercream. Drizzle the remaining blueberry reduction on top of the cake for decoration.
11. Serve and Enjoy:
    Slice the cake and enjoy the perfect combination of lemony freshness and blueberry sweetness!