Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. Sift together the cake flour and salt in a medium bowl. Set aside.

In a large mixing bowl, cream together the softened butter and granulated sugar using a hand mixer or stand mixer. Beat on medium speed for about 3-5 minutes until light and fluffy.

Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract. Slowly add the dry flour mixture and the milk to the butter mixture in three alternating additions, starting and ending with the flour. Mix gently to combine.

Divide the batter evenly between the two prepared cake pans. Smooth the tops with a spatula. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Remove the cakes from the oven and let them cool in the pans for 10 minutes. Then, turn them out onto a wire rack to cool completely.

In a medium saucepan, whisk together the eggs, sugar, lemon juice, and lemon zest. Cook over medium heat, stirring constantly until the mixture thickens and coats the back of a spoon (about 8-10 minutes).

Remove the pan from the heat and whisk in the butter until smooth. Dissolve cornstarch in a little bit of water and stir it into the lemon curd. Strain the curd through a fine mesh strainer into a bowl to remove zest and any curdled bits. Let it cool completely.

In a saucepan, combine ½ cup sugar and ¼ cup water. Heat over medium-high until the sugar dissolves and the syrup reaches 240°F (115°C) on a candy thermometer.

While the syrup is cooking, beat the egg whites in a clean mixing bowl on medium speed until they form soft peaks.

Once the sugar syrup reaches 240°F, slowly pour the hot syrup into the whipped egg whites while continuing to beat on high speed until the mixture is glossy and stiff peaks form. Reduce speed and add the remaining ½ cup sugar. Beat in the vanilla extract. Add the softened butter one tablespoon at a time, continuing to beat until smooth and fluffy.

Once the vanilla cakes have cooled completely, slice them in half horizontally to create four layers. Place one layer of cake on a serving platter and spread a layer of lemon curd on top.

Top with the next layer of cake, followed by more lemon curd. Repeat the process for the next layers.

Frost the top and sides of the cake with Italian buttercream. Garnish with additional lemon zest, if desired, and let the cake set for 30 minutes before serving for best results.