01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans; line bottoms with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt until well blended.
03 - In a large bowl, beat butter and sugar with an electric mixer on medium-high speed until light and fluffy, approximately 3 minutes.
04 - Beat in eggs one at a time, mixing thoroughly after each addition. Add lemon zest, lemon juice, and vanilla; mix until fully combined.
05 - On low speed, alternately add flour mixture and buttermilk in three additions, beginning and ending with flour. Mix just until combined, being careful not to overmix.
06 - Toss blueberries with 1 tablespoon flour in a small bowl to coat. Gently fold coated blueberries into the batter by hand.
07 - Divide batter evenly between prepared pans. Smooth tops with an offset spatula. Bake for 30-35 minutes, or until a wooden toothpick inserted in the center comes out clean.
08 - Let cakes cool in pans for 10 minutes. Run a thin knife around edges, then turn out onto wire racks to cool completely before frosting.
09 - In a large bowl, beat cream cheese and butter with an electric mixer until smooth and creamy. Gradually add powdered sugar, vanilla, lemon juice, and salt. Beat on medium-high speed until fluffy and well combined, about 2-3 minutes.
10 - Place one completely cooled cake layer on a serving plate. Spread an even layer of frosting over the top. Top with the second cake layer. Spread remaining frosting over the top and sides of the cake.
11 - Decorate with additional fresh blueberries and extra lemon zest if desired. Refrigerate until ready to serve.