Preheat oven to 350°F. Line a muffin pan with paper liners.
Sift together the powdered sugar and cake flour 3 times. Set aside.
In the bowl of a stand mixer fitted with a whisk attachment, or in a bowl with a hand-held mixer, beat the egg whites, cream of tartar and salt on medium high speed until foamy. Increase the speed to high and slowly add the granulated sugar 1 tablespoon at a time with the mixer running. Beat until glossy and soft peaks form. Stir in the vanilla.
In 3 additions, sift the dry ingredients over the meringue and gently fold in after each addition. Do not overmix or meringue will deflate.
Spoon the mixture into the prepared muffin pan, filling the cups all the way to the top. Bake until golden and spring back when touched, about 18 minutes. Let cupcakes cool completely.
To make the frosting, either in a stand mixer or with a hand-held mixer, beat the cream cheese, powdered sugar and vanilla together until smooth and creamy. Transfer to another bowl and set aside.
Add the whipping cream to the mixer bowl (no need to clean) and beat with wire whisk attachment until thickened to soft peaks.
Add cream cheese mixture in a few additions, and beat until smooth.
Frost cupcakes with buttercream and top with berries.