Preheat oven to 350 degrees Fahrenheit (with the oven rack set in the middle of the oven) and line cupcake pan with liners. Set aside.
In a medium bowl, whisk (or sift) together the dry ingredients: cake flour, baking powder, and salt. Set aside.
Add butter and granulated sugar to a large bowl. Using a hand mixer or stand mixer, cream together until light and fluffy, about one minute. Add vanilla and beat until incorporated. Then, add egg whites and beat until light and fluffy, about one minute.
Add flour mixture to butter mixture in thirds, alternating with the milk, just until each ingredient is incorporated and batter is smooth. Do not overmix.
Divide batter between 15 cupcake liners, filling each about ⅔ full. Bake in preheated oven for about 15-18 minutes, or until the center of a cupcake pops back when gently pressed down, or a toothpick comes out with crumbs (or clean). If an indent is left, or toothpick comes out with batter, cupcakes need more time.
Remove pan from oven and transfer cupcakes to a wire rack to finish cooling.
Whipped buttercream frosting
In a large bowl, add room temperature butter and beat until creamy, about one minute.
Add confectioner's sugar and slowly mix until ingredients are fully combined. Then, whip at high speed for 2-3 minutes, or until light and fluffy.
Add vanilla extract, salt, and heavy cream and whip for an additional 2 to 3 minutes, or until light and fluffy. Add additional heavy cream as needed to reach desired consistency.
Pipe or spread frosting with a knife onto cupcakes and serve.
Recipe makes enough frosting to frost 15 cupcakes with high, dramatic piped frosting (as shown in the photos), 24 cupcakes spread with a knife, a 9x13 sheet cake, or an 8-9 inch two layer cake. For a thin coating of frosting, cut recipe in half.
Buttercream frosting will begin to melt between 90 to 95 degrees Fahrenheit. If your location is nearing this temperature, I recommend refrigerating your baked goods until an hour before you're ready to serve them. Refrigerating your frosted baked goods will not hurt them, but you will want to give them some time to come to room temperature before serving.
Do not substitute cake flour with all-purpose flour - readers have reported that this gives cupcakes a 'cornbread' type texture.
Do not substitute egg whites with whole eggs. To make cupcakes with whole eggs, try my vanilla cupcakes recipe instead.