1 cup butter
1 cup all-purpose flour
1 cup white sugar
3 egg yolks
1 1/2 cups milk
6 egg whites
3 1/2 teaspoons lemon zest
2 teaspoons vanilla extract
2 tablespoons white sugar for decoration
Prepare the yeast according to package directions. Allow to stand about 5 minutes. Mix together the flour, sugar, egg yolks and water. Gradually stir the mixture into the creamed mixture until well blended. Cover the pan with plastic wrap and refrigerate overnight.
Preheat oven to 350 degrees F (175 degrees C). Grease and flour two 9-inch round cake pans.
To Make Crust: Combine butter, sugar, egg yolks, milk and lemon zest in small bowl. Stir to mix. Place 1 custard cup of filling directly on top of one of the cake layers, pressing gently. Spread evenly with sides of pan facing away from base. Place vanilla frozen cream with the top of the filling in bottom of pan. Place white sugar over filling in second layer, pressing lightly on top. Place cookies about 1 inch apart onto the prepared pan.
To Make Frosting: Beat whipping cream until stiff; beat in lemon zest and vanilla until stiff. Spread frosting over the filling and frosting on top of the filling.
Bake in the preheated oven for 30 minutes. Cool completely before cutting into squares.