• Preheat the oven to 350°F (180°C). Grease and flour a 9×13-inch cake pan. For a layer cake, line the bottoms of the cake pans with parchment paper rounds, then grease and flour the sides.
• In a medium bowl, sift together the cake flour, baking powder, baking soda, and salt. Whisk to combine and set aside.
• In another bowl, combine the buttermilk and freshly squeezed lemon juice. Whisk briefly and set aside.
• In a large mixing bowl, beat the softened butter, sugar, and lemon zest for about 2–3 minutes, or until light and fluffy.
• Add the vanilla extract. Beat in the eggs one at a time, scraping down the sides and bottom of the bowl after each addition.
• With the mixer on low, add about one-third of the dry ingredients to the butter mixture. Mix in half of the buttermilk and lemon mixture.
• Add another one-third of the dry ingredients, followed by the remaining buttermilk mixture. Finish by mixing in the final third of the dry ingredients. Stop mixing as soon as the batter comes together to avoid overmixing.
• Toss the blueberries with 2 teaspoons of flour. Gently fold them into the batter using a spatula.
• Transfer the batter to the prepared pan or pans and spread it evenly.
• Bake the Lemon Blueberry Cake for approximately 30–35 minutes in a 9×13-inch pan, or 25–30 minutes for layer cakes. The cake is ready when the top looks set and a toothpick inserted into the center comes out clean or with a few moist crumbs.
• Let the cake cool completely in the pan. If making a layer cake, allow the layers to cool fully before removing or assembling them.

Make the Cream Cheese Frosting

• Beat the softened butter until smooth and creamy.
• Add the cream cheese and beat until well combined.
• Mix in the lemon juice and 3 cups of sifted powdered sugar. Start on low speed, then increase the speed once the sugar has been incorporated.
• Gradually add more powdered sugar, about 1/2 cup at a time, until the frosting reaches your preferred sweetness and thickness.
• If the frosting becomes too thick, add whipping cream one tablespoon at a time and mix until smooth.

Decorate a 9×13-Inch Cake

• Spread the frosting evenly over the completely cooled cake.
• Garnish with fresh blueberries and thin lemon slices if desired.

Assemble a Layer Cake

• Make sure the cake layers are completely cool. For easier handling, wrap the layers and refrigerate them until slightly firm.
• If the cake layers have domed tops, carefully level them with a serrated knife or cake leveler.
• Place the first layer on a serving plate or cake stand and spread approximately 3/4 cup of frosting over the top.
• Add the second layer and frost the top with another approximately 3/4 cup of frosting. Add the final layer.
• Apply a thin layer of frosting around the entire cake to create a crumb coat. Refrigerate for about 20–30 minutes.
• Finish frosting the sides and top with the remaining frosting. Decorate with fresh blueberries if desired.
• Use a thin, sharp knife to slice and serve.