Preheat oven to 350 degrees.
Sift cake flour and all-purpose flour together into a bowl. Set aside.
Beat softened sweet and salted butters in mixer at high speed until butter is white and very fluffy, about 15 minutes.
Lower speed and add sifted sugar and blend.
Add egg yolk and vanilla and blend.
Add sifted flour mixture a cup at a time (about half). You can continue with the mixer or, for more tender cookies, remove from the mixer and continue to add flour and mix by hand until you can shape a round cookie without it sticking to your palms. You should have about 90 small, round cookies.
Place cookies on un-greased cookie sheets or parchment paper and bake until slightly brown, about 25 minutes.
Remove from the oven and let stand about 10 minutes.
Sprinkle generously with powder sugar and allow to cool. If youd like, you can put them in small paper baking cups.
3 cups all-purpose flour
¾ cup sifted powdered sugar, plus more for sprinkling
1 lb. sweet butter (unsalted)
1 stick salted butter
Yolk of 1 egg
1 tsp. vanilla
This article appears in Nov 1-30, 2010.