Preheat oven to 350 degrees F. Lightly grease & flour two 9 inch round cake pans. In a medium bowl sift together the cake flour, baking powder, and salt. In a large bowl, beat butter on medium speed for one minute. Add in sugar and beat at high speed for 3 minutes. Add in eggs, mixing until well blended. Add in lemon zest and lemon juice. Reduce speed to low and add in the flour mixture and milk, alternating with both starting and ending with the flour mixture. Divide batter evenly into cake pans, smooth tops with a spatula. Bake for 23-26 minutes or until toothpick comes out clean. Cool cakes on a wire rack for 15 minutes. Invert both cakes onto a wire rack and cool completely.

Set a fine mesh sieve over a medium bowl. In a saucepan, whisk together egg yolks and sugar until blended. Turn on heat to medium and whisk in lemon zest, lemon juice, salt, and butter. Whisk constantly for 8-10 minutes or until mixture greatly thickens. Do not let it come to a boil because it will curdle and be ruined. Immediately pour the mixture through the sieve, pressing it through with a rubber spatula. Set the hot lemon mixture bowl in a larger bowl filled partway with ice water. Do not splash water into lemon mixture. Whisk the lemon curd frequently for 15 minutes or until slightly chilled. Cover curd with plastic wrap and refrigerate.

In a large bowl, electric mix on high speed the Heavy Cream until firm peaks form. Place in a smaller bowl and refrigerate. Place softened cream cheese in the same large bowl and electric mix on medium speed for 2 minutes. Change to low speed and add vanilla and lemon curd, combine well. Gently fold in whipped cream with a spatula.

In a double boiler, whisk sugar and egg whites for 3 minutes over heat. Pour into a large bowl and electric mix the egg mixture on medium speed for 5 minutes. Add in butter, one stick at a time, mixing until smooth. Turn mixer to high speed and mix for 8 minutes. Turn mixer to medium speed and add in lemon juice and vanilla. Set aside until ready to use.

Using a long sharp serrated knife, slice each round cake horizontally in half. If the sides are to firm, cut them off and even the tops to that each layer is even. Place first layer, cut side up, on cake dish and top with Lemon Cream Cheese Filling, spreading evenly. Refrigerate for 6 minutes or until the filling is a bit firm. Add on next layer, top with Lemon Cream Cheese Filling, spreading evenly, and refrigerate for 6 minutes or until filling is firm. Repeat for third layer. Top with last layer, cut side down. Lightly frost the sides and top of cake with the Swiss Meringue Buttercream. Place in the refrigerator for 10 minutes or until the light layer is firm. This helps frost the cake more smoothly and leaves out crumbs. Frost and decorate the rest of the cake using the remaining Swiss Meringue Buttercream. Serve immediately or refrigerate the whole cake. Let stand at room temperature for 30-45 minutes before serving.