Preheat oven to 350°F. Grease three 8-inch cake pans. Line the bottom of the pans with parchment paper circles. Grease the parchment and flour the pans. Set aside.

In a small food processor combine the lemon zest with 3 or 4 tablespoons of the granulated sugar. Process until the sugar is bright yellow and the zest is in small flecks. If you don’t have a food processor combine the sugar and zest in a bowl and blend with your fingers until the zest is broken down and the sugar is bright yellow. You can also muddle the mixture using a mortar and pestle.

Combine the milk, lemon juice, egg whites and vanilla together and set aside.

Using a stand mixer fitted with the paddle attachment combine the flour, all remaining granulated sugar, lemon sugar, baking powder and salt on low until blended. With the mixer running add the butter, 1 piece at a time, and continue mixing until only pea-size pieces remain.

Pour in half the egg white mixture and increase the speed to medium-high. Beat until the mixture is light and fluffy, about 1 minute. Reduce the speed to medium-low and add the remaining egg white mixture. Blend again until combined. The batter may look slightly curdled; this is okay. Stir the batter a few times by hand using a spatula scraping the bottom and sides of the bowl until well blended. Do not overmix.

Divide the batter between the three prepared pans and smooth the tops. Bake until the tops are lightly browned and a toothpick comes out clean, about 18 to 22 minutes. Rotate the pans halfway through baking.

Cool the cakes in the pans for 10 minutes the remove and discard the parchment. Cool completely on a wire rack before frosting.

Using an electric or stand mixer beat the butter and cream cheese until smooth, about 30 seconds. Add half the Confectioners’ sugar and salt and blend on medium-low until most of the sugar is incorporated. Scrape down the sides and bottom of the bowl and blend again. Add the remaining sugar, lemon juice, vanilla and cream. Blend on medium until smooth and blended. Scrape down the bowl as needed then fold together using a spatula.

Place one cake layer on a plate or cake stand. Pipe a small border of buttercream around the outside edge of the cake to create a wall. Fill the center with about ¾ to 1 cup of lemon curd. Add another layer and repeat with a buttercream border and curd filling. Top with the final layer of cake. Frost the sides and top of the cake smoothing or decorating as desired. NOTE: If making buttercream flowers with lemon curd centers as shown in the photos, set aside about ½ cup of the curd before filling the cake layers.