Preheat the oven to 350 degrees. Line the bottom of two 9-inch round cake pans with parchment paper and coat with nonstick cooking spray. The cake can also be baked in a 9X13-inch pan (metal pan is recommended - if using glass, bake at 325 degrees F). Set aside.

In a large bowl with an electric mixer (or in the bowl of an electric mixer fitted with the paddle attachment), cream together the butter, sugar and lemon zest until light and fluffy, 3-4 minutes.

Add the eggs and vanilla and mix until well-combined, scraping down the sides of the bowl as needed.

In a separate bowl, whisk together the flour, baking powder, soda and salt. Stir the dry mixture into the wet ingredients until partly combined. Large dry streaks are ok.

Add the buttermilk and lemon juice to the batter, and stir by hand, folding the batter until just combined.

In another bowl, toss the blueberries with the 2 tablespoons flour. Add the blueberries and flour to the batter and fold in by hand with a spatula or wooden spoon until just combined. Don't over mix.

Spread the batter evenly in the prepared pans and bake for 25-35 minutes until the top springs back lightly to the touch and a toothpick inserted in the center comes out clean or with a few moist crumbs.

Let the cakes cool for 5-10 minutes in the pans before turning them out onto a cooling rack to cool completely. (I don't turn the cake out if baking in a 9X13-inch pan.)

For the frosting, whip the softened cream cheese and butter together with a handheld electric mixer or with an electric stand mixer fitted with the paddle attachment until light and fluffy, 2-3 minutes.

Add the powdered sugar, lemon zest and lemon juice and mix on low speed (so the powdered sugar doesn't fly everywhere) until it starts to come together. Increase the speed and mix until light and creamy, 2-3 minutes.

When the cake has cooled completely, place one round on a platter or plate and spread the top evenly with frosting. Place the other cake round upside down on the frosting and press just lightly. Continue frosting with a thin spatula or offset spatula until the top and sides of the cake are evenly frosted. Garnish with blueberries and lemon slices, if desired.

This cake, once frosted, lasts very well in the refrigerator for several days (I've made it up to two days in advance before serving). Take it out an hour or two before serving or serve chilled, your choice!