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 mixture. Mix just until combined, being careful not to overmix.
06 - Toss blueberries with 1 tablespoon flour in a small bowl until lightly coated. Gently fold blueberries into the batter using a spatula.
07 - Divide batter evenly between prepared pans. Smooth tops with an offset spatula.
08 - Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean. Rotate pans halfway through baking for even results.
09 - Let cakes cool in pans for 10 minutes. Run a knife around edges, then turn out onto wire racks to cool completely before frosting.
10 - In a large bowl, beat cream cheese and butter until smooth and creamy. Gradually add powdered sugar, vanilla extract, lemon juice, and salt. Beat until fluffy and spreadable.
11 - Once cakes are completely cool, spread a layer of frosting on one cake layer. Place second cake on top, then frost the top and sides evenly. Decorate with extra blueberries and lemon zest if desired.