Preheat oven to 350 degrees F. Lightly grease the bottom of two 9" round cake pans, then place a piece of parchment paper in the bottom. Liberally grease the bottoms and sides of the cake pans with cooking spray; set aside.

In the bowl of a stand mixer, cream together the butter and granulated sugar until fluffy and pale, about 5 minutes. Do not skimp on the beating time as this breaks down the sugar crystals and makes the cake fluffy. Meanwhile, in a medium to large-size bowl, whisk together the eggs, lemon juice, buttermilk, vanilla extract, and lemon zest until combined. Set aside.

In another bowl, whisk together the flour, baking powder, baking soda and salt. Starting with the flour, add a little into the stand mixer bowl with the butter mixture and beat on low speed until incorporated. Alternate adding the buttermilk mixture with the flour mixture until a thick batter comes together.

Divide the batter evenly among the baking pans and smooth out the tops. Bake for about 25-35 minutes, testing with a toothpick inserted near the center. If the toothpick comes out clean or with moist crumbs, it is done. Cool completely.

For the frosting: In the bowl of a stand mixer, cream together the butter, cream cheese, and vanilla extract until smooth, about 1 minute. Gradually add in the confectioners' sugar, alternating with the lemon juice until the frosting is light and fluffy. Beat in the lemon zest to combine.

To assemble: On a cake plate or cake stand, place one of the cake layers upside down. Pipe a thick border of frosting around the edge of the cake, leaving the center open. Fill with the lemon curd, spreading out to the frosting border. Top with the second cake layer, then frost with the remaining frosting on the tops and sides of the cake. Serve!