Preheat oven to 350 degrees. Grease and flour two 9-inch cake pans then set aside.
In a large mixing bowl, beat butter and sugar with an electric mixer for 4 minutes, scraping down the sides of the bowl with a spatula as needed.
Add eggs, one at a time, beating after each addition until well incorporated.
Add lemon zest and vanilla then beat on high speed for 2 minutes. Set aside.
In a separate bowl, sift together flour, baking powder, baking soda and salt.
Gradually add dry ingredients to wet, mixing on low speed until just barely combined.
Add lemon juice and buttermilk, mixing on low, until batter is smooth and lump free. Take care to avoid overmixing.
Distribute batter evenly among prepared cake pans.
Bake for 30-35 minutes until a toothpick inserted into the center comes out clean. Do not overbake.
Place cake pans on a wire rack to cool completely while you prepare frosting.