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 blended.
03 - In a large bowl, beat butter and sugar with an electric mixer 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, 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 until evenly distributed.
07 - Divide batter evenly between prepared pans. Smooth tops with a spatula.
08 - Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
09 - Let cakes cool in pans for 10 minutes, then turn out onto wire racks to cool completely before frosting.
10 - In a large bowl, beat cream cheese and butter until smooth. Gradually add powdered sugar, vanilla, lemon juice, and salt, beating until fluffy and spreadable.
11 - Once cakes are completely cool, spread a layer of frosting on one cake layer, top with the second cake, then frost the top and sides evenly.
12 - Decorate with extra blueberries and lemon zest if desired. Serve immediately or refrigerate until ready to serve.