01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans; line bottoms with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, baking soda, and salt.
03 - In a large bowl, beat butter and sugar with an electric mixer until light and fluffy, about 3 minutes.
04 - Beat in eggs one at a time, mixing well after each addition. Add lemon zest, lemon juice, and vanilla, mixing until combined.
05 - On low speed, alternately add flour mixture and buttermilk in 3 additions, beginning and ending with flour. Mix just until combined.
06 - Toss blueberries with 1 tablespoon flour, then gently fold into the batter.
07 - Divide batter evenly between prepared pans. Smooth tops. Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
08 - Cool cakes in pans for 10 minutes, then turn out onto wire racks to cool completely.
09 - In a large bowl, beat cream cheese and butter until smooth. Gradually add powdered sugar, vanilla, lemon juice, and salt, and beat until fluffy.
10 - Once cakes are completely cool, spread a layer of frosting on one cake layer, top with the second cake, and frost the top and sides. Decorate with extra blueberries and lemon zest if desired.