Preheat oven to 350 F, butter and lightly flour two 8-inches round cake pans and line the bottoms with parchment paper circles.
Sift together 2 cups flour, corn starch, baking powder and salt and set aside.
Stir together milk and lemon juice and set aside to curdle.
Beat butter and sugar on medium-high until pale and fluffy, about 4 minutes.
With the mixer running on low, add eggs one at a time and mix after each addition.
Add vanilla extract and lemon zest and mix to combine.
First add 1/3 of the flour mixture, then add half of the milk mixture, then 1/3 of the flour mixture, then remaining milk mixture milk, and finish with the flour mixture. Mix to combine after each addition, but do not over mix.
In a small bowl, gently toss blueberries with flour to coat, then gently fold blueberries into batter, being careful not to break the berries.
Divide batter evenly between pans, smooth the top and bake for 30-35 minutes, until toothpick inserted into center comes out clean. Cool the cakes in the pans for 10 to 15 minutes, then remove to wire rack to finish cooling.