Preheat oven to 350°F. Butter three 9-inch round baking pans and line the bottom of every with a round of parchment paper. Butter parchment paper and lightly dust pan with flour, shaking out excess.

Sift cake flour into a mixing bowl. Add all-purpose flour, baking powder, baking soda and salt and whisk for 30 seconds, set aside. In the bowl of an electrical stand mixer, fitted with the paddle attachment (if you haven’t got the paddle attachment that continually scrapes sides of the bowl while mixing, then stop mixer from time to time throughout entire mixing process and scrape down sides and bottom of bowl), whip together butter, granulated sugar and lemon zest until mixture is pale and fluffy. In a 2 cup liquid measuring cup, measure out milk then stir in sour cream and lemon juice, let rest 3 minutes.

Meanwhile, mix eggs into butter mixture one a time, then stir in lemon extract and vanilla extract. Toss blueberries with 3 tablespoons of the flour mixture. Working in three separate batches, beginning and ending with remaining flour mixture, add 1/3 of the flour mixture alternating with 1/2 of the milk mixture and mixing just until combined after each addition. Gently fold in blueberries. Divide mixture evenly amongst prepared baking pans. Bake in preheated oven until toothpick inserted into center comes out clean, about 24 – 27 minutes. Cool in baking pans about 20 – 30 minute then invert onto wire racks to cool entirely.

Once cool, frost with cream cheese frosting and decorate with blueberries and lemon slices if desired. Store in an airtight container.

ICING:
In the bowl of an electrical stand mixer fitter with the paddle attachment, whip butter until pale and fluffy. Add cream cheese and blend until smooth and fluffy. Add vanilla and lemon extract and powdered sugar and blend several minutes longer until smooth and fluffy (if frosting seems barely runny, you can chill it for a bit before frosting cake).