Preheat oven to 350°. Prep your cupcake/muffin pan with paper cups.
Sift cake flour and salt together and set aside. If using all purpose flour & cornstarch substitute (I always do) sift it together a few times. Set aside.
Separate the whites and the yolks into two separate mixing bowls.
In a clean and dry metal or glass mixing bowl, beat egg whites until stiff peaks form. Set aside.
In separate bowl, beat yolks. Slowly add sugar to yolks and beat until light and creamy.
Mix in vanilla.
Add the whites to the yolk mixture and gently blend.
Gently fold in flour mixture.
Spoon batter into the paper lined muffin cups, about 3/4 full.
Bake for 10 - 15 minutes. Tops should just start to turn golden and be springs back when touched.
Let rest for a minute or two and transfer cupcakes to wire rack. Cool.
Add jam to piping bag. I used about 1/3 cup - you may use more or less.
Instead of try to pump all the jam into the center of the cupcake, I pop the tip into 4 - 5 different spots. This way you get a bit of jam in every bite - not just a big blob of it in the center. You could go as far as measuring out jam for each cupcake, but I just estimate. I suggest to pipe a bit out into a bowl to get a feel for how the jam moves with what amount of pressure.
Wipe any excess jam off tops of cupcakes and dust with powdered sugar, if desired.
Enjoy! Store cupcakes in a covered container.