Preheat the oven to 350F (180C) degrees. Grease and flour a 9x13 inch cake pan. For a layer cake, line the bottom of the cake tins with rounds of parchment paper. Then grease and flour the sides of the pans.

In a medium bowl sift together the flour, baking powder, baking soda and salt. Whisk together and set aside.

Combine the buttermilk and freshly squeezed lemon juice. Whisk with a fork and set aside.

In a large bowl beat together the butter, sugar and lemon zest until fluffy. (About 2-3 minutes).

Add in the vanilla extract and beat in the eggs 1 at a time. Turn off the mixer and scrape down the sides of the bowl after each addition.

With the mixer on low speed, beat about 1/3 of the flour mixture into the butter mixture. Then mix in about 1/2 of the milk and lemon juice mixture. Turn off the mixer and scrape down the sides and bottom of the bowl. Repeat the process - beat in about 1/3 of the flour mixture, followed by the rest of the milk and lemon juice mixture. Lastly, beat in the last 1/3 of the flour mixture. Do not overmix.

Toss the blueberries with the 2 teaspoons of flour, then gently fold into the batter with a spatula or rubber spoon.

Pour the batter into the prepared pan/pans. Bake for 30-35 minutes for a 9x13 inch pan, or about 25-30 minutes for layer cakes. When done baking, the top should look set and an inserted toothpick comes out clean. If you gently press on the top of the cake it should feel firm and slightly springy to the touch, but not gooey.

Cool the cakes in the pan. If making a layer cake, be careful when inserting the pans. Do not try to invert the cake pans while they are still hot.

Beat the butter until soft, then mix in the cream cheese.

Add in the lemon juice and mix in 3 cups of the powdered sugar, starting with the mixer on low speed and then turning up to medium as it starts to combine.

Beat in the rest of the powdered sugar about 1/2 cup at a time until the desired sweetness and thickness is reached. If the frosting seems too thick, beat in 1 tablespoon whipping cream.

For a 9x13 inch cake, frost the cooled cake and optionally decorate with blueberries and lemon slices.

For a layer cake, ensure that the layers are fully cooled first. If the tops are domed, use a serrated knife or cake leveler to gently cut off the rounded top. Place one cake layer on the plate or cake stand that you plan to serve it on. Frost the top with about 3/4 cup frosting. Place the second cake layer on top and frost the top with another 3/4 cup of frosting. Then place the third cake layer on top. Frost the sides of the cake with a thin layer of frosting (the crumb coat) and place in the fridge for about 20-30 minutes. Once the thin layer of frosting has hardened, frost the sides and top of the cake with swirls of frosting. Optionally, decorate with blueberries.

Slice with a thin, sharp knife.