01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans, lining bottoms with parchment paper.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl until thoroughly combined.
03 - Beat butter and sugar with an electric mixer on medium-high speed until light and fluffy, approximately 3 minutes.
04 - Add eggs one at a time, mixing well after each addition. Incorporate lemon zest, lemon juice, and vanilla extract until fully combined.
05 - On low speed, alternately add flour mixture and buttermilk in three additions, beginning and ending with flour. Mix until just combined, being careful not to overmix.
06 - Toss blueberries with 1 tablespoon flour to prevent sinking, then gently fold into the batter using a spatula.
07 - Divide batter evenly between prepared pans and smooth tops. Bake for 30-35 minutes until a toothpick inserted in the center emerges clean.
08 - Let cakes cool in pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
09 - Beat cream cheese and butter until smooth and creamy. Gradually add powdered sugar, vanilla, lemon juice, and salt, beating until light and fluffy.
10 - Spread a layer of frosting on one cooled cake layer, place the second cake on top, then frost the top and sides evenly. Decorate with additional blueberries and lemon zest if desired.