Lemon Curd
3/4 cup lemon juice
2 tablespoons cornstarch
1 cup + 2 tablespoons sugar
3 eggs
6 egg yolks
1/2 cup + 1 tablespoon butter, cut into small pieces
2 tablespoons grated lemon peel
Frosting
1/2 cup heavy whipping cream
4.5 ounces chopped white chocolate
1 3/4 cups heavy whipping cream
3/4 teaspoon vanilla extract
Cake
2 3/4 cups sifted flour
1 teaspoon baking powder
3/4 teaspoon salt
4 ounces chopped white chocolate
1/2 cup heavy whipping cream
1/2 cup + 2 tablespoons milk
1/2 cup heavy whipping cream
1 teaspoon vanilla extract
1/2 cup softened butter
1 cup sugar
4 eggs yolks
4 egg whites
1 cup sugar

Lemon Curd
Combine lemon juice and cornstarch in heavy medium saucepan, stirring till cornstarch dissolves. Whisk in remaining ingredients. Cook over medium heat 7 minutes till mixture is thick and smooth and just begins to boil, stirring constantly. Transfer to medium bowl. Place plastic wrap directly on surface of curd to prevent skin from forming. Refrigerate 6 hours till chilled.
Frosting
Melt together cream and chocolate, stirring till smooth. Whisk in cream and vanilla. Refrigerate 6 hours till well chilled.
Cake
Heat oven to 350°F. Butter three 9 inch round cake pans with 1 1/2 inch high sides. Line bottoms with waxed paper. Butter paper. Dust pans with flour and tap out excess. Sift flour, baking powder and salt together into medium bowl. Repeat sifting. Melt together chocolate and cream, stirring till smooth. Mix in milk, cream and vanilla. Beat butter and sugar together till fluffy. Beat in yolks. Stir dry ingredients into butter mixture alternately with white chocolate mixture, beginning and ending with dry ingredients. With clean dry beaters, beat egg whites to soft peaks. Gradually beat in sugar. Continue beating till stiff but not dry. Fold whites into cake batter in 2 additions. Divide batter among prepared pans. Bake 24 minutes till toothpick inserted in center comes out clean and cakes are beginning to pull away from sides of pans. Cool cakes in pans on racks 10 minutes. Turn cakes out onto racks, peel off waxed paper and cool completely. Beat frosting till stiff peaks form. Place 1 cake layer on platter. Spread 2/3 cup lemon curd evenly atop cake layer. Spread 3/4 cup frosting atop curd. Top with second cake layer. Spread cake with 2/3 cup curd, then with 3/4 cup frosting. Top with third cake layer. Frost top and sides of entire cake evenly with 3 cups frosting. Place remaining lemon curd in pastry bag fitted with No. 2 star tip. Pipe circle of curd around top of cake, 1/2 inch from edge. Pipe evenly spaced diagonal lines inside circle, creating lattice pattern. Reserve remaining curd for another use. Spoon remaining frosting into pastry bag fitted with No. 2 star tip. Pipe ruffled border around top and bottom edges of cake. Can be prepared up to 6 hours ahead. Refrigerate and let stand at room temperature 30 minutes before serving.