Step 1: Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans, or line bottoms with parchment paper.
Step 2: In a medium bowl, whisk together the sifted cake flour, baking powder, baking soda, and salt. Set aside.
Step 3: In a large bowl, using an electric mixer, cream the softened butter and granulated sugar together until light and fluffy (about 3-5 minutes).
Step 4: Add the eggs one at a time, beating well after each addition until fully incorporated. Stir in the lemon zest.
Step 5: In a separate small bowl, combine the buttermilk and lemon juice.
Step 6: Alternately add the dry ingredients and the buttermilk mixture to the butter-sugar mixture, beginning and ending with the dry ingredients. Mix on low speed until just combined, being careful not to overmix.
Step 7: Gently fold in the floured blueberries by hand until evenly distributed throughout the batter.
Step 8: Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Step 9: Let the cake layers cool in the pans for 10-15 minutes before inverting them onto a wire rack to cool completely. Ensure cakes are completely cool before frosting.
Step 10: Prepare the frosting: In a large bowl, beat the softened cream cheese and butter together until smooth and creamy. Gradually add the sifted powdered sugar, lemon juice, and vanilla extract, beating until light and fluffy. If frosting is too thick, add a tiny bit more lemon juice or milk; if too thin, add more powdered sugar.
Step 11: Once the cake layers are completely cool, assemble and frost the cake as desired. Garnish with extra lemon zest or fresh blueberries, if desired. Serve and enjoy!