01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans, then line bottoms with parchment paper.
02 - Whisk together flour, baking powder, baking soda, and salt in a medium bowl until well combined.
03 - Beat butter and granulated sugar with an electric mixer on medium-high speed until light and fluffy, approximately 3 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Mix in lemon zest, lemon juice, and vanilla extract until fully incorporated.
05 - On low speed, alternately add flour mixture and buttermilk in three portions, beginning and ending with flour. Mix just until combined; avoid overmixing.
06 - Toss blueberries with 1 tablespoon flour, then gently fold into the batter using a spatula.
07 - Divide batter evenly between prepared pans and smooth tops. Bake for 30 to 35 minutes, or until a wooden 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. Gradually add powdered sugar, vanilla, lemon juice, and salt; continue beating until fluffy and spreadable.
10 - Place one cooled cake layer on serving plate. Spread frosting evenly over top, position second layer, then frost top and sides of entire cake.