Preheat oven to 350 degrees F. Line two 9-inch round cake pans with parchment paper circles and spray with baking spray.
In a large bowl, beat the butter, sugar, and lemon zest until creamy and light, about 2 to 3 minutes.
Add eggs, lemon juice, and vanilla extract, scraping the sides of the bowl and mixing until combined.
Add the flour, baking powder, baking soda, and salt alternately with the buttermilk in 2-3 additions, mixing between each addition to combine.
Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes until a toothpick inserted into the center of the cakes comes out clean with just a few crumbs clinging to it.
Cool completely before leveling the tops of the cakes and decorating with lemon buttercream frosting.
Beat the butter until creamy and smooth using a hand mixer or a stand mixer fitted with the whisk attachment.
Gradually add the powdered sugar along with the lemon zest. Add enough heavy cream and lemon juice to get and nice, spreadable frosting. Beat for 3 to 4 minutes until creamy and light.
