• Preheat the oven to 350°F (180°C). Grease and flour a 9×13-inch baking pan. For a layer cake, line the bottoms of the cake pans with parchment paper, then grease and flour the sides.
• Sift the cake flour, baking powder, baking soda, and salt into a medium bowl. Whisk briefly to combine and set aside.
• In a separate bowl or measuring jug, whisk together the buttermilk and fresh lemon juice. Set aside.
• In a large mixing bowl, beat the softened butter, granulated sugar, and lemon zest for 2–3 minutes, until pale and fluffy.
• Mix in the vanilla extract. Add the eggs one at a time, beating after each addition. Scrape down the sides and bottom of the bowl as necessary.
• With the mixer on low speed, add about one-third of the dry ingredients. Mix in half of the buttermilk-lemon mixture, followed by another third of the dry ingredients. Add the remaining liquid mixture and finish with the remaining flour mixture. Mix only until combined.
• Toss the fresh blueberries with 2 teaspoons of flour. Gently fold them into the batter using a spatula. This helps distribute the berries throughout the Lemon Blueberry Cake.
• Transfer the batter to the prepared pan or divide it evenly among the prepared layer cake pans.
• Bake a 9×13-inch cake for approximately 30–35 minutes. For cake layers, bake for approximately 25–30 minutes. The cake is ready when the top is set and a toothpick inserted near the center comes out clean or with a few moist crumbs.
• Allow the cake to cool completely before frosting. Layer cakes should be handled particularly carefully while warm because the soft crumb can break easily.

Make the Cream Cheese Frosting

• Beat the softened butter until smooth and creamy. Add the cream cheese and mix until combined.
• Beat in the fresh lemon juice.
• Gradually add the sifted powdered sugar, beginning with the mixer on low speed. Increase to medium speed once the sugar is incorporated.
• Continue adding powdered sugar about 1/2 cup at a time until the frosting reaches your preferred sweetness and consistency.
• If the frosting is too thick, mix in whipping cream a little at a time until smooth and spreadable.

Decorate the Cake

• For a 9×13-inch cake, spread the frosting evenly over the completely cooled cake. Garnish with fresh blueberries and thin lemon slices if desired.
• For a lemon blueberry layer cake, cool the layers completely before assembling. Chilling the layers can make them easier to handle. Level any domed tops with a serrated knife if necessary.
• Place the first layer on a serving plate or cake stand and spread about 3/4 cup frosting over the top. Repeat with the second layer, then add the final layer.
• Spread a thin crumb coat over the outside of the cake and refrigerate for 20–30 minutes. Finish with the remaining frosting and decorate with fresh blueberries as desired.