2-3/4 cup sifted cake flour
1 tablespoon baking powder
1/2 teaspoon salt
1/2 cup unsalted butter, softened
1-1/2 cup granulated sugar
1 teaspoon vanilla extract
4 egg whites
1 cup milk
Old Fashioned Buttercream
Position a rack in the center of the oven and preheat to 350ºF. Grease and flour two 9 inch cake pans, tapping out excess flour.
In a medium sized bowl sift together the flour, baking powder, and salt.
In a large bowl combine the butter and sugar and beat with an electric mixer until well combined. Add the vanilla and egg whites and beat at high speed until light, about 2 minutes. Beat in half of thee dry ingredients, just until blended. Beat in all the milk and then the remaining dry ingredients. Beat one minute and then turn into the prepared pans, dividing up the batter equally. Smooth the tops with a spatula and firmly tap pans on the surface to level. Bake on same shelf until the tops spring back when lightly touched and a toothpick comes out clean, 30 to 35 minutes. Cool in the pans on a rack for 10 minutes and then invert onto racks. Return one layer to an upright position and cool both layers to room temperature.
Place one layer bottom side up on a serving dish and spread with 1 cup of Old fashioned Buttercream. Add the second layer, right side up, over the Buttercream. Spread top and then sides with remaining Buttercream.
3 tablespoon potato starch
1 cup cold milk
2 egg yolks
1-1/2 cup sifted confectioner’s sugar
1-1/4 cup unsalted butter, softened
1 tablespoon vanilla extract
Place the potato starch in a small heavy saucepan. Gradually whisk in the milk until smooth, then whisk in the egg yolks and 1 cup of the confectioner’s sugar. Place over moderately low heat, stirring constantly, cook until mixture becomes very thick and begins to boil, about 10 minutes. Turn this buttercream base into a shallow dish, cover with plastic placed directly on the surface, and cool to room temperature.
In a large bowl combine the butter and the remaining 1/2 cup confectioner’s sugar; beat until light and fluffy, 1 to 2 minutes. Using an electric mixer with a very strong motor, preferably an upright model, beat in the buttercream base bit by bit, beating until smooth. Beat in the vanilla. Use to frost cakes at room temperature; the frosting will set when chilled.