Preheat your oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. Line the bottoms with parchment paper circles.

In a medium bowl, whisk together the 2 3/4 cups all-purpose flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, using an electric mixer, cream together the softened unsalted butter and granulated sugar on medium-high speed until light and fluffy, about 3-5 minutes. Scrape down the sides of the bowl as needed.

Add the eggs one at a time, beating well after each addition until fully incorporated. Beat in the lemon zest and vanilla extract.

In a separate small bowl or measuring cup, combine the buttermilk and fresh lemon juice. With the mixer on low speed, alternately add the dry ingredients and the buttermilk mixture to the wet ingredients, beginning and ending with the dry ingredients (e.g., 1/3 dry, 1/2 wet, 1/3 dry, 1/2 wet, 1/3 dry). Mix until just combined; do not overmix.

In a small bowl, toss the fresh blueberries with the reserved 2 tablespoons of flour. Gently fold the floured blueberries into the cake batter using a rubber spatula until evenly distributed.

Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. The tops should be lightly golden and spring back when gently touched.

Remove the cakes from the oven and let them cool in the pans for 10-15 minutes before inverting them onto a wire rack to cool completely. Ensure cakes are entirely cool before frosting (this can take 1-2 hours).

In a large mixing bowl, using an electric mixer, beat the softened cream cheese and softened unsalted butter together on medium speed until smooth and creamy, about 2-3 minutes. Ensure there are no lumps of cream cheese.

Gradually add the sifted powdered sugar, 1 cup at a time, beating on low speed until combined, then increasing to medium-high until smooth. Scrape down the sides of the bowl often.

Add the fresh lemon juice, lemon zest, vanilla extract, and pinch of salt. Beat on medium-high speed for another 1-2 minutes until the frosting is light, fluffy, and well combined. Taste and adjust lemon juice or powdered sugar if desired.

Once the cake layers are completely cool, place one layer on your serving plate or cake stand. Spread about 1 to 1 1/2 cups of frosting evenly over the top.

Carefully place the second cake layer on top. Spread the remaining frosting over the top and sides of the cake, smoothing it with an offset spatula or knife.

Garnish with fresh blueberries, thin lemon slices, and extra lemon zest, if desired.

Refrigerate the cake for at least 30 minutes before slicing to allow the frosting to set. Serve chilled or at room temperature.