Preheat your oven to 325 degrees F. Spray two 8-inch round cake pans with nonstick spray, line the bottoms with parchment paper and spray again. Set aside.
In a medium size bowl, whisk together the cake flour, pistachios, baking powder, lemon zest, and salt. Set aside.
In a bowl of an electric mixer fitted with a paddle attachment, beat the butter and sugar together on medium-high speed for 3 to 5 minutes, until the texture is lighter in color and smooth in texture.
With the mixer on medium speed, gradually add the egg whites. Make sure to scrape down the sides and bottom of the bowl between additions. When all of the egg whites are added, turn your mixer to medium-high speed and beat the batter for an additional 2 to 3 minutes. At this point, the texture should be smooth and the mixture should have nearly doubled in volume.
As the batter mixes, combine the buttermilk and lemon juice.
With the mixer on low speed on low speed, alternately add the dry ingredients and the buttermilk mixture to the butter mixture, starting and ending with the dry ingredients. Scrape down the sides and bottom of the bowl to ensure all the batter has been incorporated. Stir for an additional 30 seconds.
Divide batter evenly in the two pans, about 25 to 26 ounces of batter in each 8-inch pan.
Bake the cakes until a toothpick comes out with a few crumbs inserted into the center, about 35 minutes. Let cool on wire racks for 10 minutes before inverting them onto cooling racks to cool completely.
Once the layers are cooled completely, carefully divide the cake layers in half horizontally, creating two thin layers from each cake.