Preheat oven to 350 degrees F. Butter the bottom and sides of three (6-inch) cake pans. Line the bottom of each pan with aparchment paper round.
Add cake flour, baking powder, and sea salt to a small mixing bowl. Whisk to combine. Set aside.
Add fresh lemon juice to milk and set aside for several minutes.
Add unsalted butter and granulated sugar to stand mixer. Beat on medium high speed for about 3 minutes.
Add eggs one at a time, beating on low after each addition for about 30 seconds, or until incorporated.
Add vanilla bean paste and fresh lemon zest. Beat on low for about 15 seconds, or until incorporated.
Add half the flour mixture. Beat on low, just until incorporated, about 30 seconds. Add half the milk mixture. Beat on low, just until incorporated, about 30 seconds. Repeat process with remaining flour and milk mixtures. Avoid over mixing.
Add blueberries and cake flour to small bowl. Toss gently to combine.
Remove bowl from stand mixer. Fold blueberries into cake batter using large spatula.
Transfer cake batter to prepared cake pans. Bake cakes in preheated oven for 30 minutes or until they are golden along the edges, firm to the touch, and a toothpick interested into the center comes out clean.
Remove cake pans from oven and cool completely. Invert pans and remove cakes.