01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans, then line bottoms with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt until well combined.
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 extract, mixing until fully incorporated.
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, then gently fold into the batter using a spatula until evenly distributed.
07 - Divide batter evenly between prepared pans. Smooth tops with a 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, then carefully turn out onto wire racks to cool completely before frosting.
09 - In a large bowl, beat cream cheese and butter until smooth and creamy. Gradually add powdered sugar, vanilla extract, lemon juice, and salt. Beat on medium speed until fluffy and spreadable.
10 - Once cakes are completely cool, spread an even layer of frosting on one cake layer. Place second cake on top and frost the top and sides of the entire cake. Decorate with additional blueberries and lemon zest if desired.