Preheat oven to 350 degrees. Line cupcake or muffin tins with papers; set aside. Into a medium bowl, sift together cake flour, baking powder, and salt. Combine milk and vanilla in a glass measuring cup.Advertisement
Place butter in the bowl of an electric mixer fitted with the paddle attachment, and beat until pale and creamy. With mixer on medium speed, gradually add sugar in a steady stream; continue beating until light and fluffy, about 3 minutes. Reduce speed to low.
Add flour mixture to butter mixture in three batches, alternating with the milk mixture and starting and ending with the flour. Do not overbeat.
In a clean bowl of electric mixer fitted with the whisk attachment, beat egg whites on medium-high speed until stiff peaks form. Fold one-third of the whites into flour mixture to lighten. Fold in remaining egg whites in two batches, being careful not to deflate the whites.
Pour batter into prepared tins, filling cups to about 1/2 inch from the tops. Bake until a cake tester inserted near the centers comes out clean and the tops spring back when pressed lightly in the center, 18 to 20 minutes. Remove from oven; let cool completely before icing or storing.
For best results, make the cupcakes the day before serving. If time does not permit, you may bake them up to three weeks in advance; wrap well in plastic, and store in the freezer. Remove them from the freezer at least two hours before you plan to ice and assemble cake.