preheat oven to 360 degrees F – 170 degrees C – grease and flour two 7 inch round pans mix together the flour baking powder and salt set aside
in a large bowl cream together the butter and sugar until light and fluffy about 6 minutes beat in the eggs one at a time then stir in the vanilla beat in the flour mixture alternately with the milk mixture just until incorporated
pour batter into prepared pans bake in the preheated oven for 35 minutes or until a toothpick inserted into the center of the cake comes out clean Allow to cool in pans on wire racks for 15 minutes then invert onto wire racks to cool completely
to make filling- in medium saucepan mix together 1 tablespoon lemon zest 1/3 cup lemon juice and 1 tablespoon cornstarch until smooth mix in 5 tablespoons butter and 3/4 cup sugar and bring mixture to boil over medium heat boil for one minute stirring constantly in a small bowl with a wire whisk beat egg yolks until smooth whisk in a small amount of the hot lemon mixture pour the egg mixture into the saucepan beating the hot lemon
mixture rapidly reduce heat to low cook stirring constantly 5 minutes or until thick – not to boil –pour the mixture into medium bowl press plastic wrap onto surface to keep skin from forming as it cools cool to room temperature refrigerate 2 hours
to make the frosting- in large bowl beat confectioners sugar 1/3 cup butter 3 tablespoons lemon juice and 1 teaspoon lemon zest until smooth beat in milk and increase speed and continue to beat until light and fluffy
to assemble- with long serrated knife split each cake layer in half horizontally making 5 layers place 1 layer cut side up on a serving plate spread with half of the lemon filling top with another layer and spread with 1/3 cup frosting add the third layer and spread with remaining half of the lemon filling press on final cake layer and frost top and sides of the cake with remaining frosting refrigerate the cake until serving time.