In a small bowl, combine flour, baking powder, and salt.
In a stand mixer, beat egg whites and cream of tartar until stiff but not dry.
While the egg whites are mixing, beat egg yolks until frothy and lighter yellow.
Slowly add vanilla and sugar, mix until mixture has doubled.
Fold in egg whites slowly, followed by the flour mixture.
Spray delectoval pan generously with cake spray.
Fill pan 1/3 full and bake for 8 minutes, or until sides are slightly browned and springy to the touch.
Let cool on a cookie rack in the pan and then slide cakes out using a knife to loosen from pan (if necessary.)
While cooling mix filling ingredients until light and fluffy. Using a Bismarck Tip #230, pipe filling into your cakes from the bottom of the cake in 3-4 places along the cake. This spreads best if done when cool or icing will melt into cake.